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title: "Aboutness"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Aboutness"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T07:22:24.487269+00:00"
instance: "kb-cron"
---
Aboutness is a term used in library and information science (LIS), linguistics, philosophy of language, and philosophy of mind. In general, the term refers to the concept that a text, utterance, image, or action is on or of something. In LIS, it is often considered synonymous with a document's subject. In the philosophy of mind, it has been often considered synonymous with intentionality, perhaps since John Searle (1983). In the philosophy of logic and language, it is understood as the way a piece of text relates to a subject matter or topic.
R. A. Fairthorne (1969) is credited with coining the exact term "aboutness", which became popular in LIS since the late 1970s, perhaps due to arguments put forward by William John Hutchins (1975, 1977, 1978). Hutchins argued that "aboutness" was to be preferred to "subject" because it removed some epistemological problems. Birger Hjørland (1992, 1997) argued, however, that the same epistemological problems also were present in Hutchins' proposal, why "aboutness" and "subject" should be considered synonymous.
While information scientists may well be concerned with the literary aboutness (John Hutchins, 1975, 1977, 1978), philosophers of mind and psychologists with the psychological or intentional aboutness (John Searle, 1983) and language of thought (Jerry Fodor, 1975), and semantic externalists with the external state of affairs (Hilary Putnam, 1975). These seminal perspectives are respectively analogous to Ogden and Richards' Literary, psychological, and external contexts (1923), as well as Karl Popper's World 1, 2, and 3 (1977).
== See also ==
Content analysis
Intentional stance
Theme and rheme
== Literature ==
Furner, J. (November 5, 2006). "The ontology of subjects of works". ASIS&T conference.
Hjørland, B. (2001). "Towards a theory of aboutness, subject, topicality, theme, domain, field, content... and relevance". Journal of the American Society for Information Science and Technology, 52(9), 774–778.
Bruza, P. D., Song, D. W., & Wong, K. F. (2000). "Aboutness from a commonsense perspective". Journal of the American Society for Information Science, 51(12), 1090–1105. Available at: http://people.kmi.open.ac.uk/dawei/papers/aboutness-aista00.pdf
Campbell, G. (2000a). "Aboutness and meaning: How a paradigm of subject analysis can illuminate queer theory in literary studies". IN: CAIS 2000. Canadian Association for Information Science: Proceedings of the 28th Annual Conference.
Campbell, G. (2000b). "Queer theory and the creation of contextual subject access tools for gay and lesbian communities". Knowledge Organization, 27(3), 122–131.
Hjørland, B. (1997): Information seeking and subject representation: An activity-theoretical approach to information science. Westport & London: Greenwood Press.
Holley, R., and Joudrey, D.N. (2021). "Aboutness and Conceptual Analysis: A Review", Cataloging & Classification Quarterly 59:2-3, 159–185.
Joudrey, D. N. (2005). Building Puzzles And Growing Pearls: A Qualitative Exploration Of Determining Aboutness (PhD diss.: University of Pittsburgh).
Heidegger, M. (1996). Being and Time, trans. by Joan Stambaugh. Albany: State University of New York Press.
Hjørland, B. (1992). "The concept of "subject" in information science". Journal of Documentation, 48(2), 172–200.
Frohmann, B. (1990). "Rules of indexing: A critique of mentalism in information retrieval theory". Journal of Documentation, 81–101.
Beghtol, C. (1986). "Bibliographic classification theory and text linguistics: aboutness analysis, intertextuality and the cognitive act of classifying documents". Journal of Documentation, 42, 84–113.
Searle, John (1983). Intentionality: An Essay in the Philosophy of Mind, Cambridge University Press.
Salem, Shawky (1982). "Towards "coring" and "aboutness": An approach to some aspects of in-depth indexing". Journal of Information Science Principles & Practice, 1982, 4, 167–170.
Mark Petersen, A. (1979). "The meaning of "about" in fiction indexing and retrieval". ASLIB Proceedings, 31, 251- 257.
Swift, D. F., Winn, V. & Bramer, D. (1978). ""Aboutness" as a strategy for retrieval in the social sciences". ASLIB Proceedings, 30, 182–187.
Hutchings, W. J. (1978). "The concept of "aboutness" in subject indexing". ASLIB Proceedings, 30, 172–181.
Hutchins, W. J. (1977). "On the problem of "aboutness" in document analysis". Journal of Informatics, 1, 17–35.
Maron, M. E. (1977). "On indexing, retrieval and the meaning of about". Journal of the American Society for Information Science, 28, 38–43.
Heidegger, M. (1977). "Sein und Zeit", in Heidegger's Gesamtausgabe, volume 2, ed. F.-W. von Herrmann, 1977, XIV, 586p.
Hutchins, W. J. (1975). Languages of indexing and classification. A linguistic study of structures and functions. London: Peter Peregrinus.
Fairthorne, R. A. (1969). "Content analysis, specification and control". Annual Review of Information Science and Technology, 4, 73–109.
Heidegger, M. (1962). Being and Time, trans. by John Macquarrie & Edward Robinson. London: SCM Press.
Goodman, N. (1961). "About". Mind, 70(277), 1-24.
Putnam, H. (1958). "Formalization of the concept "about"". Philosophy of Science, 25(2), 125-130.
Thalheimer, R. (1936). "More about "about"". Analysis, 3(3): 46-48.
Ryle, G. (1933). "About". Analysis, 1(1): 10–11.
Yablo, S. (2014) Aboutness, Princeton University Press
== References ==

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title: "Abstract nonsense"
chunk: 1/1
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tags: "science, encyclopedia"
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instance: "kb-cron"
---
In mathematics, abstract nonsense, general abstract nonsense, generalized abstract nonsense, and general nonsense are nonderogatory terms used by mathematicians to describe long, theoretical parts of a proof they skip over when readers are expected to be familiar with them. These terms are mainly used for abstract methods related to category theory and homological algebra. More generally, "abstract nonsense" may refer to a proof that relies on category-theoretic methods, or even to the study of category theory itself.
== Background ==
Roughly speaking, category theory is the study of the general form, that is, categories of mathematical theories, without regard to their content. As a result, mathematical proofs that rely on category-theoretic ideas often seem out-of-context, somewhat akin to a non sequitur. Authors sometimes dub these proofs "abstract nonsense" as a light-hearted way of alerting readers to their abstract nature. Labeling an argument "abstract nonsense" is usually not intended to be derogatory, and is instead used jokingly, in a self-deprecating way, affectionately, or even as a compliment to the generality of the argument. Alexander Grothendieck was critical of this notion, and stated that:
The introduction of the cipher 0 or the group concept was general nonsense too, and mathematics was more or less stagnating for thousands of years because nobody was around to take such childish steps...
Certain ideas and constructions in mathematics share a uniformity throughout many domains, unified by category theory. Typical methods include the use of classifying spaces and universal properties, use of the Yoneda lemma, natural transformations between functors, and diagram chasing.
When an audience can be assumed to be familiar with the general form of such arguments, mathematicians will use the expression "Such and such is true by abstract nonsense" rather than provide an elaborate explanation of particulars. For example, one might say that "By abstract nonsense, products are unique up to isomorphism when they exist", instead of arguing about how these isomorphisms can be derived from the universal property that defines the product. This allows one to skip proof details that can be considered trivial or not providing much insight, focusing instead on genuinely innovative parts of a larger proof.
== History ==
The term predates the foundation of category theory as a subject itself. Referring to a joint paper with Samuel Eilenberg that introduced the notion of a "category" in 1942, Saunders Mac Lane wrote the subject was 'then called "general abstract nonsense"'. The term is often used to describe the application of category theory and its techniques to less abstract domains.
The term is believed to have been coined by the mathematician Norman Steenrod, himself one of the developers of the categorical point of view.
== Notes and references ==
== External links ==
Usage in mathematical exposition from Noam Elkies' class notes

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instance: "kb-cron"
---
In mathematics and related fields, an abstract structure is a way of describing a set of mathematical objects and the relationships between them, focusing on the essential rules and properties rather than any specific meaning or example.
For example, in a game such as chess, the rules of how the pieces move and interact define the structure of the game, regardless of whether the pieces are made of wood or plastic. Similarly, an abstract structure defines a framework of objects, operations, and relationships. These structures are studied in their own right, revealing fundamental mathematical principles. While a real-world object or computer program might represent, instantiate, or implement an abstract structure, the structure itself exists as an abstract concept, independent of any particular representation.
This abstraction allows to see common patterns across seemingly different areas of mathematics and to apply the same reasoning and tools to analyze them. Abstract structures are studied not only in logic and mathematics but in the fields that apply them, as computer science and computer graphics, and in the studies that reflect on them, such as philosophy (especially the philosophy of mathematics).
An abstract structure has a richer structure than a concept or an idea. An abstract structure must include precise rules of behaviour which can be used to determine whether a candidate implementation actually matches the abstract structure in question, and it must be free from contradictions. Thus we may debate how well a particular government fits the concept of democracy, but there is no room for debate over whether a given sequence of moves is or is not a valid game of chess (for example Kasparovian approaches).
== Examples ==
A sorting algorithm is an abstract structure, but a recipe is not, because it depends on the properties and quantities of its ingredients.
A simple melody is an abstract structure, but an orchestration is not, because it depends on the properties of particular instruments.
Euclidean geometry is an abstract structure, but the theory of continental drift is not, because it depends on the geology of the Earth.
A formal language is an abstract structure, but a natural language is not, because its rules of grammar and syntax are open to debate and interpretation.
== Notes ==
== See also ==
Abstraction in computer science
Abstraction in general
Abstraction in mathematics
Abstract object
Deductive apparatus
Formal sciences
Mathematical structure

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instance: "kb-cron"
---
Abstraction in mathematics is the process of extracting the underlying structures, patterns or properties of a mathematical concept, removing any dependence on real world objects with which it might originally have been connected, and generalizing it so that it has wider applications or matching among other abstract descriptions of equivalent phenomena. In other words, to be abstract is to remove context and application. Two of the most highly abstract areas of modern mathematics are category theory and model theory.
== Description ==
Many areas of mathematics began with the study of real world problems, before the underlying rules and concepts were identified and defined as abstract structures. For example, geometry has its origins in the calculation of distances and areas in the real world, and algebra started with methods of solving problems in arithmetic.
Abstraction is an ongoing process in mathematics and the historical development of many mathematical topics exhibits a progression from the concrete to the abstract. For example, the first steps in the abstraction of geometry were historically made by the ancient Greeks, with Euclid's Elements being the earliest extant documentation of the axioms of plane geometry—though Proclus tells of an earlier axiomatisation by Hippocrates of Chios. In the 17th century, Descartes introduced Cartesian co-ordinates which allowed the development of analytic geometry. Further steps in abstraction were taken by Lobachevsky, Bolyai, Riemann and Gauss, who generalised the concepts of geometry to develop non-Euclidean geometries. Later in the 19th century, mathematicians generalised geometry even further, developing such areas as geometry in n dimensions, projective geometry, affine geometry and finite geometry. Finally Felix Klein's "Erlangen program" identified the underlying theme of all of these geometries, defining each of them as the study of properties invariant under a given group of symmetries. This level of abstraction revealed connections between geometry and abstract algebra.
In mathematics, abstraction can be advantageous in the following ways:
It reveals deep connections between different areas of mathematics.
Known results in one area can suggest conjectures in another related area.
Techniques and methods from one area can be applied to prove results in other related areas.
Patterns from one mathematical object can be generalized to other similar objects in the same class.
On the other hand, abstraction can also be disadvantageous in that highly abstract concepts can be difficult to learn. A degree of mathematical maturity and experience may be needed for conceptual assimilation of abstractions.
Bertrand Russell, in The Scientific Outlook (1931), writes that "Ordinary language is totally unsuited for expressing what physics really asserts, since the words of everyday life are not sufficiently abstract. Only mathematics and mathematical logic can say as little as the physicist means to say."
== See also ==
Abstract detail
Generalization
Abstract thinking
Abstract logic
Abstract algebraic logic
Abstract model theory
Abstract nonsense
Concept
Mathematical maturity
== References ==
== Further reading ==
Bajnok, Béla (2013). An Invitation to Abstract Mathematics. Springer. ISBN 978-1-4614-6635-2.

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title: "Abuse of notation"
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instance: "kb-cron"
---
In mathematics, abuse of notation occurs when an author uses a mathematical notation in a way that is not entirely formally correct, but which might help to simplify the exposition or to suggest the correct intuition, while possibly minimizing errors and confusion at the same time.
A closely related concept is abuse of language or abuse of terminology, where a term — rather than a notation — is used informally. For example, while the word representation properly designates a group homomorphism from a group G to GL(V), where V is a vector space, it is common to call V itself a "representation of G."
Since both mathematical notation and terminology vary across time and context, what is flagged as abuse in one context could be formally correct in another. Furthermore, abuse of notation should not be conflated with misuse of notation, which does not have the presentational benefits of the former and should be avoided, such as the misuse of constants of integration.
== Examples ==
=== Suppression of parameters ===
Many mathematical objects consist of a set, often called the underlying set, equipped with some additional structure, such as a mathematical operation or a topology. It is a common abuse of notation to use the same symbol for the underlying set and the structured object, a phenomenon known as suppression of parameters.
For example,
Z
{\displaystyle \mathbb {Z} }
may denote the set of the integers, the group of integers together with addition, or the ring of integers with addition and multiplication. Likewise,
R
3
{\displaystyle \mathbb {R} ^{3}}
is often used to mean 3D Euclidean space taken as a vector space, metric space, or topological space, depending on the properties relevant in context. This is because, for example, the Euclidean distance is understood to be the 'default' metric on
R
3
{\displaystyle \mathbb {R} ^{3}}
and is assumed when not stated otherwise, even though there are others.
Similarly, while a topological space
(
X
,
T
)
{\displaystyle (X,{\mathcal {T}})}
consists of both an underlying set
X
{\displaystyle X}
and a topology
T
{\displaystyle {\mathcal {T}}}
, it is customary to talk about "the space
X
{\displaystyle X}
" in situations where only one topology on
X
{\displaystyle X}
is ever considered — once that topology is clearly established.
In general, there is no problem with suppression of parameters if the object under reference is well understood, and avoiding such an abuse of notation might even make mathematical texts more pedantic and more difficult to read. When this abuse of notation may be confusing, one may distinguish between structures by denoting e.g.
(
Z
,
+
)
{\displaystyle (\mathbb {Z} ,+)}
the group of integers with addition and
(
Z
,
+
,
⋅
)
{\displaystyle (\mathbb {Z} ,+,\cdot )}
the ring of integers; by explicitly defining the topology, metric structure, etc. of interest on
R
3
{\displaystyle \mathbb {R} ^{3}}
; or by explicitly writing out tuples like
(
X
,
T
)
{\displaystyle (X,{\mathcal {T}})}
and
(
X
,
T
′
)
{\displaystyle (X,{\mathcal {T'}})}
to distinguish between different topological spaces with the same underlying set.
=== Function notation ===
One may encounter, in many textbooks, sentences such as "Let
f
(
x
)
{\displaystyle f(x)}
be a function ...". This is an abuse of notation, as the name of the function is
f
,
{\displaystyle f,}
and
f
(
x
)
{\displaystyle f(x)}
denotes the value of
f
{\displaystyle f}
for the element
x
{\displaystyle x}
of its domain. More precisely correct phrasings include "Let
f
{\displaystyle f}
be a function of the variable
x
{\displaystyle x}
..." or "Let
x
↦
f
(
x
)
{\displaystyle x\mapsto f(x)}
be a function ..." This abuse of notation is widely used, as it simplifies the formulation, and the systematic use of a correct notation quickly becomes pedantic.
Another abuse of notation occurs in sentences such as "Let us consider the function
x
2
+
x
+
1
{\displaystyle x^{2}+x+1}
...", when in fact
x
2
+
x
+
1
{\displaystyle x^{2}+x+1}
is a polynomial expression, not a function per se — whereas the function that maps the variable
x
{\displaystyle x}
to
x
2
+
x
+
1
{\displaystyle x^{2}+x+1}
could formally be denoted
x
↦
x
2
+
x
+
1.
{\displaystyle x\mapsto x^{2}+x+1.}
Similarly, a constant function
f
{\displaystyle f}
may be identified with its value, as in
f
=
c
{\displaystyle f=c}
, when it would be more correct to write e.g. "
f
(
x
)
=
c
{\displaystyle f(x)=c}
for all inputs
x
{\displaystyle x}
." Nevertheless, these abuses of notation are widely used, since they are more concise and generally not confusing.
=== Equality vs. isomorphism ===
Many mathematical structures are defined through a characterizing property (often a universal property). Once this desired property is defined, there may be various ways to construct the structure, and the corresponding results are formally different objects, but which have exactly the same properties (i.e., isomorphic). As there is no way to distinguish these isomorphic objects through their properties, it is standard to consider them as equal, even if this is formally wrong.
One example of this is the Cartesian product, which is often seen as associative:

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title: "Abuse of notation"
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category: "reference"
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date_saved: "2026-05-05T07:22:55.629926+00:00"
instance: "kb-cron"
---
(
E
×
F
)
×
G
=
E
×
(
F
×
G
)
=
E
×
F
×
G
{\displaystyle (E\times F)\times G=E\times (F\times G)=E\times F\times G}
.
But this is strictly speaking not true: if
x
∈
E
{\displaystyle x\in E}
,
y
∈
F
{\displaystyle y\in F}
and
z
∈
G
{\displaystyle z\in G}
, the identity
(
(
x
,
y
)
,
z
)
=
(
x
,
(
y
,
z
)
)
{\displaystyle ((x,y),z)=(x,(y,z))}
would imply that
(
x
,
y
)
=
x
{\displaystyle (x,y)=x}
and
z
=
(
y
,
z
)
{\displaystyle z=(y,z)}
, and so
(
(
x
,
y
)
,
z
)
=
(
x
,
y
,
z
)
{\displaystyle ((x,y),z)=(x,y,z)}
would mean nothing. However, these equalities can be legitimized and made rigorous in category theory—using the idea of a natural isomorphism.
Another example of similar abuses occurs in statements such as "there are two non-Abelian groups of order 8", which more strictly stated means "there are two isomorphism classes of non-Abelian groups of order 8".
=== Equivalence classes ===
Referring to an equivalence class of an equivalence relation by
x
{\displaystyle x}
instead of
[
x
]
{\displaystyle [x]}
is an abuse of notation. Formally, if a set
X
{\displaystyle X}
is partitioned by an equivalence relation
∼
{\displaystyle \sim }
, then for each
x
∈
X
{\displaystyle x\in X}
, the equivalence class
{
y
∈
X
|
y
∼
x
}
{\displaystyle \{y\in X|y\sim x\}}
is denoted
[
x
]
{\displaystyle [x]}
. But in practice, if the remainder of the discussion is focused on the equivalence classes rather than the individual elements of the underlying set, then it is common to drop the square brackets in the discussion.
For example, in modular arithmetic, a finite group of order
n
{\displaystyle n}
can be formed by partitioning the integers via the equivalence relation "
x
∼
y
{\displaystyle x\sim y}
if and only if
x
≡
y
(
m
o
d
n
)
{\displaystyle x\equiv y\ (\mathrm {mod} \ n)}
". The elements of that group would then be
[
0
]
,
[
1
]
,
…
,
[
n
−
1
]
{\displaystyle [0],[1],\dots ,[n-1]}
, but in practice they are usually denoted simply as
0
,
1
,
.
.
.
,
n
−
1
{\displaystyle 0,1,...,n-1}
.
Another example is the space of (classes of) measurable functions over a measure space, or classes of Lebesgue integrable functions, where the equivalence relation is equality "almost everywhere".
== Subjectivity ==
The terms "abuse of language" and "abuse of notation" depend on context. Writing "f : A → B" for a partial function from A to B is almost always an abuse of notation, but not in a category theoretic context, where f can be seen as a morphism in the category of sets and partial functions.
== See also ==
Mathematical notation
Misnomer
== References ==

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title: "Active and passive transformation"
chunk: 1/2
source: "https://en.wikipedia.org/wiki/Active_and_passive_transformation"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T07:22:56.857340+00:00"
instance: "kb-cron"
---
Geometric transformations can be distinguished into two types: active or alibi transformations which change the physical position of a set of points relative to a fixed frame of reference or coordinate system (alibi meaning "being somewhere else at the same time"); and passive or alias transformations which leave points fixed but change the frame of reference or coordinate system relative to which they are described (alias meaning "going under a different name").
For instance, active transformations are useful to describe successive positions of a rigid body. On the other hand, passive transformations may be useful in human motion analysis to observe the motion of the tibia relative to the femur, that is, its motion relative to a (local) coordinate system which moves together with the femur, rather than a (global) coordinate system which is fixed to the floor.
In three-dimensional Euclidean space, any proper rigid transformation, whether active or passive, can be represented as a screw displacement, the composition of a translation along an axis and a rotation about that axis.
The terms active transformation and passive transformation were first introduced in 1957 by Valentine Bargmann for describing Lorentz transformations in special relativity.
== Example ==
As an example, let the vector
v
=
(
v
1
,
v
2
)
∈
R
2
{\displaystyle \mathbf {v} =(v_{1},v_{2})\in \mathbb {R} ^{2}}
, be a vector in the plane. A rotation of the vector through an angle θ in counterclockwise direction is given by the rotation matrix:
R
=
(
cos
⁡
θ
−
sin
⁡
θ
sin
⁡
θ
cos
⁡
θ
)
,
{\displaystyle R={\begin{pmatrix}\cos \theta &-\sin \theta \\\sin \theta &\cos \theta \end{pmatrix}},}
which can be viewed either as an active transformation or a passive transformation (where the above matrix will be inverted), as described below.
== Spatial transformations in the Euclidean space R3 ==
In general a spatial transformation
T
:
R
3
→
R
3
{\displaystyle T\colon \mathbb {R} ^{3}\to \mathbb {R} ^{3}}
may consist of a translation and a linear transformation. In the following, the translation will be omitted, and the linear transformation will be represented by a 3×3 matrix
T
{\displaystyle T}
.
=== Active transformation ===
As an active transformation,
T
{\displaystyle T}
transforms the initial vector
v
=
(
v
x
,
v
y
,
v
z
)
{\displaystyle \mathbf {v} =(v_{x},v_{y},v_{z})}
into a new vector
v
′
=
(
v
x
′
,
v
y
′
,
v
z
′
)
=
T
v
=
T
(
v
x
,
v
y
,
v
z
)
{\displaystyle \mathbf {v} '=(v'_{x},v'_{y},v'_{z})=T\mathbf {v} =T(v_{x},v_{y},v_{z})}
.
If one views
{
e
x
′
=
T
(
1
,
0
,
0
)
,
e
y
′
=
T
(
0
,
1
,
0
)
,
e
z
′
=
T
(
0
,
0
,
1
)
}
{\displaystyle \{\mathbf {e} '_{x}=T(1,0,0),\ \mathbf {e} '_{y}=T(0,1,0),\ \mathbf {e} '_{z}=T(0,0,1)\}}
as a new basis, then the coordinates of the new vector
v
′
=
v
x
e
x
′
+
v
y
e
y
′
+
v
z
e
z
′
{\displaystyle \mathbf {v} '=v_{x}\mathbf {e} '_{x}+v_{y}\mathbf {e} '_{y}+v_{z}\mathbf {e} '_{z}}
in the new basis are the same as those of
v
=
v
x
e
x
+
v
y
e
y
+
v
z
e
z
{\displaystyle \mathbf {v} =v_{x}\mathbf {e} _{x}+v_{y}\mathbf {e} _{y}+v_{z}\mathbf {e} _{z}}
in the original basis. Note that active transformations make sense even as a linear transformation into a different vector space. It makes sense to write the new vector in the unprimed basis (as above) only when the transformation is from the space into itself.
=== Passive transformation ===
On the other hand, when one views
T
{\displaystyle T}
as a passive transformation, the initial vector
v
=
(
v
x
,
v
y
,
v
z
)
{\displaystyle \mathbf {v} =(v_{x},v_{y},v_{z})}
is left unchanged, while the coordinate system and its basis vectors are transformed in the opposite direction, that is, with the inverse transformation
T
−
1
{\displaystyle T^{-1}}
. This gives a new coordinate system XYZ with basis vectors:
e
X
=
T
−
1
(
1
,
0
,
0
)
,
e
Y
=
T
−
1
(
0
,
1
,
0
)
,
e
Z
=
T
−
1
(
0
,
0
,
1
)
{\displaystyle \mathbf {e} _{X}=T^{-1}(1,0,0),\ \mathbf {e} _{Y}=T^{-1}(0,1,0),\ \mathbf {e} _{Z}=T^{-1}(0,0,1)}
The new coordinates
(
v
X
,
v
Y
,
v
Z
)
{\displaystyle (v_{X},v_{Y},v_{Z})}
of
v
{\displaystyle \mathbf {v} }
with respect to the new coordinate system XYZ are given by:
v
=
(
v
x
,
v
y
,
v
z
)
=
v
X
e
X
+
v
Y
e
Y
+
v
Z
e
Z
=
T
−
1
(
v
X
,
v
Y
,
v
Z
)
.
{\displaystyle \mathbf {v} =(v_{x},v_{y},v_{z})=v_{X}\mathbf {e} _{X}+v_{Y}\mathbf {e} _{Y}+v_{Z}\mathbf {e} _{Z}=T^{-1}(v_{X},v_{Y},v_{Z}).}
From this equation one sees that the new coordinates are given by
(
v
X
,
v
Y
,
v
Z
)
=
T
(
v
x
,
v
y
,
v
z
)
.
{\displaystyle (v_{X},v_{Y},v_{Z})=T(v_{x},v_{y},v_{z}).}
As a passive transformation
T
{\displaystyle T}
transforms the old coordinates into the new ones.
Note the equivalence between the two kinds of transformations: the coordinates of the new point in the active transformation and the new coordinates of the point in the passive transformation are the same, namely
(
v
X
,
v
Y
,
v
Z
)
=
(
v
x
′
,
v
y
′
,
v
z
′
)
.
{\displaystyle (v_{X},v_{Y},v_{Z})=(v'_{x},v'_{y},v'_{z}).}
== In abstract vector spaces ==

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The distinction between active and passive transformations can be seen mathematically by considering abstract vector spaces.
Fix a finite-dimensional vector space
V
{\displaystyle V}
over a field
K
{\displaystyle K}
(thought of as
R
{\displaystyle \mathbb {R} }
or
C
{\displaystyle \mathbb {C} }
), and a basis
B
=
{
e
i
}
1
≤
i
≤
n
{\displaystyle {\mathcal {B}}=\{e_{i}\}_{1\leq i\leq n}}
of
V
{\displaystyle V}
. This basis provides an isomorphism
C
:
K
n
→
V
{\displaystyle C:K^{n}\rightarrow V}
via the component map
(
v
i
)
1
≤
i
≤
n
=
(
v
1
,
⋯
,
v
n
)
↦
∑
i
v
i
e
i
{\textstyle (v_{i})_{1\leq i\leq n}=(v_{1},\cdots ,v_{n})\mapsto \sum _{i}v_{i}e_{i}}
.
An active transformation is then an endomorphism on
V
{\displaystyle V}
, that is, a linear map from
V
{\displaystyle V}
to itself. Taking such a transformation
τ
∈
End
(
V
)
{\displaystyle \tau \in {\text{End}}(V)}
, a vector
v
∈
V
{\displaystyle v\in V}
transforms as
v
↦
τ
v
{\displaystyle v\mapsto \tau v}
. The components of
τ
{\displaystyle \tau }
with respect to the basis
B
{\displaystyle {\mathcal {B}}}
are defined via the equation
τ
e
i
=
∑
j
τ
j
i
e
j
{\textstyle \tau e_{i}=\sum _{j}\tau _{ji}e_{j}}
. Then, the components of
v
{\displaystyle v}
transform as
v
i
↦
τ
i
j
v
j
{\displaystyle v_{i}\mapsto \tau _{ij}v_{j}}
.
A passive transformation is instead an endomorphism on
K
n
{\displaystyle K^{n}}
. This is applied to the components:
v
i
↦
T
i
j
v
j
=:
v
i
′
{\displaystyle v_{i}\mapsto T_{ij}v_{j}=:v'_{i}}
. Provided that
T
{\displaystyle T}
is invertible, the new basis
B
′
=
{
e
i
′
}
{\displaystyle {\mathcal {B}}'=\{e'_{i}\}}
is determined by asking that
v
i
e
i
=
v
i
′
e
i
′
{\displaystyle v_{i}e_{i}=v'_{i}e'_{i}}
, from which the expression
e
i
′
=
(
T
−
1
)
j
i
e
j
{\displaystyle e'_{i}=(T^{-1})_{ji}e_{j}}
can be derived.
Although the spaces
End
(
V
)
{\displaystyle {\text{End}}(V)}
and
End
(
K
n
)
{\displaystyle {\text{End}}({K^{n}})}
are isomorphic, they are not canonically isomorphic. Nevertheless a choice of basis
B
{\displaystyle {\mathcal {B}}}
allows construction of an isomorphism.
=== As left- and right-actions ===
Often one restricts to the case where the maps are invertible, so that active transformations are the general linear group
GL
(
V
)
{\displaystyle {\text{GL}}(V)}
of transformations while passive transformations are the group
GL
(
n
,
K
)
{\displaystyle {\text{GL}}(n,K)}
.
The transformations can then be understood as acting on the space of bases for
V
{\displaystyle V}
. An active transformation
τ
∈
GL
(
V
)
{\displaystyle \tau \in {\text{GL}}(V)}
sends the basis
{
e
i
}
↦
{
τ
e
i
}
{\displaystyle \{e_{i}\}\mapsto \{\tau e_{i}\}}
. Meanwhile a passive transformation
T
∈
GL
(
n
,
K
)
{\displaystyle T\in {\text{GL}}(n,K)}
sends the basis
{
e
i
}
↦
{
∑
j
(
T
−
1
)
j
i
e
j
}
{\textstyle \{e_{i}\}\mapsto \left\{\sum _{j}(T^{-1})_{ji}e_{j}\right\}}
.
The inverse in the passive transformation ensures the components transform identically under
τ
{\displaystyle \tau }
and
T
{\displaystyle T}
. This then gives a sharp distinction between active and passive transformations: active transformations act from the left on bases, while the passive transformations act from the right, due to the inverse.
This observation is made more natural by viewing bases
B
{\displaystyle {\mathcal {B}}}
as a choice of isomorphism
Φ
B
:
K
n
→
V
{\displaystyle \Phi _{\mathcal {B}}:K^{n}\rightarrow V}
. The space of bases is equivalently the space of such isomorphisms, denoted
Iso
(
K
n
,
V
)
{\displaystyle {\text{Iso}}(K^{n},V)}
. Active transformations, identified with
GL
(
V
)
{\displaystyle {\text{GL}}(V)}
, act on
Iso
(
K
n
,
V
)
{\displaystyle {\text{Iso}}(K^{n},V)}
from the left by composition, that is if
τ
{\displaystyle \tau }
represents an active transformation, we have
Φ
B
′
=
τ
∘
Φ
B
{\displaystyle \Phi _{\mathcal {B'}}=\tau \circ \Phi _{\mathcal {B}}}
. On the opposite, passive transformations, identified with
GL
(
n
,
K
)
{\displaystyle {\text{GL}}(n,K)}
acts on
Iso
(
K
n
,
V
)
{\displaystyle {\text{Iso}}(K^{n},V)}
from the right by pre-composition, that is if
T
{\displaystyle T}
represents a passive transformation, we have
Φ
B
″
=
Φ
B
∘
T
{\displaystyle \Phi _{\mathcal {B''}}=\Phi _{\mathcal {B}}\circ T}
.
This turns the space of bases into a left
GL
(
V
)
{\displaystyle {\text{GL}}(V)}
-torsor and a right
GL
(
n
,
K
)
{\displaystyle {\text{GL}}(n,K)}
-torsor.
From a physical perspective, active transformations can be characterized as transformations of physical space, while passive transformations are characterized as redundancies in the description of physical space. This plays an important role in mathematical gauge theory, where gauge transformations are described mathematically by transition maps which act from the right on fibers.
== See also ==
Change of basis
Covariance and contravariance of vectors
Rotation of axes
Translation of axes
== References ==
Dirk Struik (1953) Lectures on Analytic and Projective Geometry, page 84, Addison-Wesley.
== External links ==
UI ambiguity

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Adequality is a technique developed by Pierre de Fermat in his treatise Methodus ad disquirendam maximam et minimam (a Latin treatise circulated in France c. 1636 ) to calculate maxima and minima of functions, tangents to curves, area, center of mass, least action, and other problems in calculus. According to André Weil, Fermat "introduces the technical term adaequalitas, adaequare, etc., which he says he has borrowed from Diophantus. As Diophantus V.11 shows, it means an approximate equality, and this is indeed how Fermat explains the word in one of his later writings." (Weil 1973). Diophantus coined the word παρισότης (parisotēs) to refer to an approximate equality. Claude Gaspard Bachet de Méziriac translated Diophantus's Greek word into Latin as adaequalitas. Paul Tannery's French translation of Fermat's Latin treatises on maxima and minima used the words adéquation and adégaler.
== Fermat's method ==
Fermat used adequality first to find maxima of functions, and then adapted it to find tangent lines to curves.
To find the maximum of a term
p
(
x
)
{\displaystyle p(x)}
, Fermat equated (or more precisely adequated)
p
(
x
)
{\displaystyle p(x)}
and
p
(
x
+
e
)
{\displaystyle p(x+e)}
and after doing algebra he could cancel out a factor of
e
,
{\displaystyle e,}
and then discard any remaining terms involving
e
.
{\displaystyle e.}
To illustrate the method by Fermat's own example, consider the problem of finding the maximum of
p
(
x
)
=
b
x
−
x
2
{\displaystyle p(x)=bx-x^{2}}
(in Fermat's words, it is to divide a line of length
b
{\displaystyle b}
at a point
x
{\displaystyle x}
, such that the product of the two resulting parts be a maximum). Fermat adequated
b
x
−
x
2
{\displaystyle bx-x^{2}}
with
b
(
x
+
e
)
−
(
x
+
e
)
2
=
b
x
−
x
2
+
b
e
−
2
e
x
−
e
2
{\displaystyle b(x+e)-(x+e)^{2}=bx-x^{2}+be-2ex-e^{2}}
. That is (using the notation
∽
{\displaystyle \backsim }
to denote adequality, introduced by Paul Tannery):
b
x
−
x
2
∽
b
x
−
x
2
+
b
e
−
2
e
x
−
e
2
.
{\displaystyle bx-x^{2}\backsim bx-x^{2}+be-2ex-e^{2}.}
Canceling terms and dividing by
e
{\displaystyle e}
Fermat arrived at
b
∽
2
x
+
e
.
{\displaystyle b\backsim 2x+e.}
Removing the terms that contained
e
{\displaystyle e}
Fermat arrived at the desired result that the maximum occurred when
x
=
b
/
2
{\displaystyle x=b/2}
.
Fermat also used his principle to give a mathematical derivation of Snell's laws of refraction directly from the principle that light takes the quickest path.
== Descartes' criticism ==
Fermat's method was highly criticized by his contemporaries, particularly Descartes. Victor Katz suggests this is because Descartes had independently discovered the same new mathematics, known as his method of normals, and Descartes was quite proud of his discovery. Katz also notes that while Fermat's methods were closer to the future developments in calculus, Descartes' methods had a more immediate impact on the development.
== Scholarly controversy ==
Both Newton and Leibniz referred to Fermat's work as an antecedent of infinitesimal calculus. Nevertheless, there is disagreement amongst modern scholars about the exact meaning of Fermat's adequality. Fermat's adequality was analyzed in a number of scholarly studies. In 1896, Paul Tannery published a French translation of Fermat's Latin treatises on maxima and minima (Fermat, Œuvres, Vol. III, pp. 121–156). Tannery translated Fermat's term as “adégaler” and adopted Fermat's “adéquation”. Tannery also introduced the symbol
∽
{\displaystyle \backsim }
for adequality in mathematical formulas.
Heinrich Wieleitner (1929) wrote:Fermat replaces A with A+E. Then he sets the new expression roughly equal (angenähert gleich) to the old one, cancels equal terms on both sides, and divides by the highest possible power of E. He then cancels all terms which contain E and sets those that remain equal to each other. From that [the required] A results. That E should be as small as possible is nowhere said and is at best expressed by the word "adaequalitas". (Wieleitner uses the symbol
∼
{\displaystyle \scriptstyle \sim }
.)
Max Miller (1934) wrote:Thereupon one should put the both terms, which express the maximum and the minimum, approximately equal (näherungsweise gleich), as Diophantus says.(Miller uses the symbol
≈
{\displaystyle \scriptstyle \approx }
.)
Jean Itard (1948) wrote:One knows that the expression "adégaler" is adopted by Fermat from Diophantus, translated by Xylander and by Bachet. It is about an approximate equality (égalité approximative) ". (Itard uses the symbol
∽
{\displaystyle \scriptstyle \backsim }
.)
Joseph Ehrenfried Hofmann (1963) wrote:Fermat chooses a quantity h, thought as sufficiently small, and puts f(x + h) roughly equal (ungefähr gleich) to f(x). His technical term is adaequare.(Hofmann uses the symbol
≈
{\displaystyle \scriptstyle \approx }
.)
Peer Strømholm (1968) wrote:The basis of Fermat's approach was the comparition of two expressions which, though they had the same form, were not exactly equal. This part of the process he called "comparare par adaequalitatem" or "comparer per adaequalitatem", and it implied that the otherwise strict identity between the two sides of the "equation" was destroyed by the modification of the variable by a small amount:
f
(
A
)
∼
f
(
A
+
E
)
{\displaystyle \scriptstyle f(A){\sim }f(A+E)}
.

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This, I believe, was the real significance of his use of Diophantos' πἀρισον, stressing the smallness of the variation. The ordinary translation of 'adaequalitas' seems to be "approximate equality", but I much prefer "pseudo-equality" to present Fermat's thought at this point.He further notes that "there was never in M1 (Method 1) any question of the variation E being put equal to zero. The words Fermat used to express the process of suppressing terms containing E was 'elido', 'deleo', and 'expungo', and in French 'i'efface' and 'i'ôte'. We can hardly believe that a sane man wishing to express his meaning and searching for words, would constantly hit upon such tortuous ways of imparting the simple fact that the terms vanished because E was zero.(p. 51)
Claus Jensen (1969) wrote:Moreover, in applying the notion of adégalité – which constitutes the basis of Fermat's general method of constructing tangents, and by which is meant a comparition of two magnitudes as if they were equal, although they are in fact not ("tamquam essent aequalia, licet revera aequalia non sint") – I will employ the nowadays more usual symbol
≈
{\displaystyle \scriptstyle \approx }
. The Latin quotation comes from Tannery's 1891 edition of Fermat, volume 1, page 140.
Michael Sean Mahoney (1971) wrote:Fermat's Method of maxima and minima, which is clearly applicable to any polynomial P(x), originally rested on purely finitistic algebraic foundations. It assumed, counterfactually, the inequality of two equal roots in order to determine, by Viete's theory of equations, a relation between those roots and one of the coefficients of the polynomial, a relation that was fully general. This relation then led to an extreme-value solution when Fermat removed his counterfactual assumption and set the roots equal. Borrowing a term from Diophantus, Fermat called this counterfactual equality 'adequality'.(Mahoney uses the symbol
≈
{\displaystyle \scriptstyle \approx }
.) On p. 164, end of footnote 46, Mahoney notes that one of the meanings of adequality is approximate equality or equality in the limiting case.
Charles Henry Edwards, Jr. (1979) wrote:For example, in order to determine how to subdivide a segment of length
b
{\displaystyle \scriptstyle b}
into two segments
x
{\displaystyle \scriptstyle x}
and
b
−
x
{\displaystyle \scriptstyle b-x}
whose product
x
(
b
−
x
)
=
b
x
−
x
2
{\displaystyle \scriptstyle x(b-x)=bx-x^{2}}
is maximal, that is to find the rectangle with perimeter
2
b
{\displaystyle \scriptstyle 2b}
that has the maximal area, he [Fermat] proceeds as follows. First he substituted
x
+
e
{\displaystyle \scriptstyle x+e}
(he used A, E instead of x, e) for the unknown x, and then wrote down the following "pseudo-equality" to compare the resulting expression with the original one:
b
(
x
+
e
)
−
(
x
+
e
)
2
=
b
x
+
b
e
−
x
2
−
2
x
e
−
e
2
∼
b
x
−
x
2
.
{\displaystyle \scriptstyle b(x+e)-(x+e)^{2}=bx+be-x^{2}-2xe-e^{2}\;\sim \;bx-x^{2}.}
After canceling terms, he divided through by e to obtain
b
−
2
x
−
e
∼
0.
{\displaystyle \scriptstyle b-2\,x-e\;\sim \;0.}
Finally he discarded the remaining term containing e, transforming the pseudo-equality into the true equality
x
=
b
2
{\displaystyle \scriptstyle x={\frac {b}{2}}}
that gives the value of x which makes
b
x
−
x
2
{\displaystyle \scriptstyle bx-x^{2}}
maximal. Unfortunately, Fermat never explained the logical basis for this method with sufficient clarity or completeness to prevent disagreements between historical scholars as to precisely what he meant or intended."
Kirsti Andersen (1980) wrote:The two expressions of the maximum or minimum are made "adequal", which means something like as nearly equal as possible.(Andersen uses the symbol
≈
{\displaystyle \scriptstyle \approx }
.)
Herbert Breger (1994) wrote:I want to put forward my hypothesis: Fermat used the word "adaequare" in the sense of "to put equal" ... In a mathematical context, the only difference between "aequare" and "adaequare" seems to be that the latter gives more stress on the fact that the equality is achieved.(Page 197f.)
John Stillwell (Stillwell 2006 p. 91) wrote:Fermat introduced the idea of adequality in 1630s but he was ahead of his time. His successors were unwilling to give up the convenience of ordinary equations, preferring to use equality loosely rather than to use adequality accurately. The idea of adequality was revived only in the twentieth century, in the so-called non-standard analysis.
Enrico Giusti (2009) cites Fermat's letter to Marin Mersenne where Fermat wrote:Cette comparaison par adégalité produit deux termes inégaux qui enfin produisent l'égalité (selon ma méthode) qui nous donne la solution de la question" ("This comparison by adequality produces two unequal terms which finally produce the equality (following my method) which gives us the solution of the problem").. Giusti notes in a footnote that this letter seems to have escaped Breger's notice.
Klaus Barner (2011) asserts that Fermat uses two different Latin words (aequabitur and adaequabitur) to replace the nowadays usual equals sign, aequabitur when the equation concerns a valid identity between two constants, a universally valid (proved) formula, or a conditional equation, adaequabitur, however, when the equation describes a relation between two variables, which are not independent (and the equation is no valid formula). On page 36, Barner writes: "Why did Fermat continually repeat his inconsistent procedure for all his examples for the method of tangents? Why did he never mention the secant, with which he in fact operated? I do not know."
Katz, Schaps, Shnider (2013) argue that Fermat's application of the technique to transcendental curves such as the cycloid shows that Fermat's technique of adequality goes beyond a purely algebraic algorithm, and that, contrary to Breger's interpretation, the technical terms parisotes as used by Diophantus and adaequalitas as used by Fermat both mean "approximate equality". They develop a formalisation of Fermat's technique of adequality in modern mathematics as the standard part function which rounds off a finite hyperreal number to its nearest real number.
== See also ==
Fermat's principle
Transcendental law of homogeneity
== References ==
== Bibliography ==
Breger, Herbert (1994). "The mysteries of adaequare: A vindication of fermat". Archive for History of Exact Sciences. 46 (3): 193–219. doi:10.1007/BF01686277. S2CID 119440472.
Edwards, C. H. (1979). The Historical Development of the Calculus. doi:10.1007/978-1-4612-6230-5. ISBN 978-0-387-94313-8.
Giusti, E. (2009) "Les méthodes des maxima et minima de Fermat", Ann. Fac. Sci. Toulouse Math. (6) 18, Fascicule Special, 59–85.
Grabiner, Judith V. (Sep 1983), "The Changing Concept of Change: The Derivative from Fermat to Weierstrass", Mathematics Magazine, 56 (4): 195–206, doi:10.2307/2689807, JSTOR 2689807
Katz, V. (2008), A History of Mathematics: An Introduction, Addison Wesley
Stillwell, J.(2006) Yearning for the impossible. The surprising truths of mathematics, page 91, A K Peters, Ltd., Wellesley, MA.
Weil, A., Book Review: The mathematical career of Pierre de Fermat. Bull. Amer. Math. Soc. 79 (1973), no. 6, 1138–1149.

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In mathematics, the term adjoint applies in several situations. Several of these share a similar formalism: if A is adjoint to B, then there is typically some formula of the type
(Ax, y) = (x, By).
Specifically, adjoint or adjunction may mean:
Adjoint of a linear map, also called its transpose in case of matrices
Hermitian adjoint (adjoint of a linear operator) in functional analysis
Adjoint endomorphism of a Lie algebra
Adjoint representation of a Lie group
Adjoint functors in category theory
Adjunction (field theory)
Adjunction formula (algebraic geometry)
Adjunction space in topology
Conjugate transpose of a matrix in linear algebra
Adjugate matrix, related to its inverse
Adjoint equation
The upper and lower adjoints of a Galois connection in order theory
The adjoint of a differential operator with general polynomial coefficients
Kleisli adjunction
Monoidal adjunction
Quillen adjunction
Axiom of adjunction in set theory
Adjunction (rule of inference)

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In information science, authority control is a process that organizes information, for example in library catalogs, by using a single, distinct spelling of a name (heading) or an identifier (generally persistent and alphanumeric) for each topic or concept. The word authority in authority control derives from the idea that the names of people, places, things, and concepts are authorized, i.e., they are established in one particular form. These one-of-a-kind headings or identifiers are applied consistently throughout catalogs which make use of the respective authority file, and are applied for other methods of organizing data such as linkages and cross references. Each controlled entry is described in an authority record in terms of its scope and usage, and this organization helps the library staff maintain the catalog and make it user-friendly for researchers.
Catalogers assign each subject—such as author, topic, series, or corporation—a particular unique identifier or heading term which is then used consistently, uniquely, and unambiguously for all references to that same subject, which removes variations from different spellings, transliterations, pen names, or aliases. The unique header can guide users to all relevant information including related or collocated subjects. Authority records can be combined into a database and called an authority file, and maintaining and updating these files as well as "logical linkages" to other files within them is the work of librarians and other information catalogers. Accordingly, authority control is an example of controlled vocabulary and of bibliographic control.
While in theory any piece of information is amenable to authority control such as personal and corporate names, uniform titles, series names, and subjects, library catalogers typically focus on author names and titles of works. Since 1898, one of the most commonly used authority files globally is the subject headings from the Library of Congress.
As time passes, information changes, prompting needs for reorganization. According to one view, authority control is not about creating a perfect seamless system but rather it is an ongoing effort to keep up with these changes and try to bring "structure and order" to the task of helping users find information.
== Benefits of authority control ==
Better researching. Authority control helps researchers understand a specific subject with less wasted effort. A well-designed digital catalog/database enables a researcher to query a few words of an entry to bring up the already established term or phrase, thus improving accuracy and saving time.
Makes searching more predictable. It can be used in conjunction with keyword searching using "and" or "not" or "or" or other Boolean operators on a web browser. It increases chances that a given search will return relevant items.
Consistency of records.
Organization and structure of information.
Efficiency for catalogers. The process of authority control is not only of great help to researchers searching for a particular subject to study, but it can help catalogers organize information as well. Catalogers can use authority records when trying to categorize new items, since they can see which records have already been cataloged and can therefore avoid unnecessary work.
Maximizes library resources. Authority control helps ensure libraries have an accurate inventory of their materials, so that, for example, duplicate orders are not placed for an already owned resource.
Fewer errors. It can help catch errors caused by typos or misspellings which can sometimes accumulate over time, sometimes known as quality drift. These errors can then be corrected by library staff or by automated clean-up software.
== Examples ==
=== Diverse names describe the same subject ===
Sometimes within a catalog, there are diverse names or spellings for only one person or subject. This variation may cause researchers to overlook relevant information. Authority control is used by catalogers to collocate materials that logically belong together but that present themselves differently. Records are used to establish uniform titles that collocate all versions of a given work under one unique heading even when such versions are issued under different titles. With authority control, one unique preferred name represents all variations and will include different variations, spellings and misspellings, uppercase versus lowercase variants, differing dates, and so forth. For example, in Wikipedia, the first wife of Charles III is described by an article Diana, Princess of Wales as well as numerous other descriptors, e.g. Princess Diana, but both Princess Diana and Diana, Princess of Wales describe the same person so they all redirect to the same main article; in general, all authority records choose one title as the preferred one for consistency. In an online library catalog, various entries might look like the following:
Diana. (1)
Diana, Princess of Wales. (1)
Diana, Princess of Wales, 1961–1997. (13)
Diana, Princess of Wales 1961–1997. (1)
Diana, Princess of Wales, 1961–1997. (2)
DIANA, PRINCESS OF WALES, 1961–1997. (1)
These terms describe the same person. Accordingly, authority control reduces these entries to one unique entry or officially authorized heading, sometimes termed an access point: Diana, Princess of Wales, 1961–1997.

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Generally, there are different authority file headings and identifiers used by different libraries in different countries, possibly inviting confusion, but there are different approaches internationally to try to lessen the confusion. One international effort to prevent such confusion is the Virtual International Authority File which is a collaborative attempt to provide a single heading for a particular subject. It is a way to standardize information from different authority files around the world such as the Integrated Authority File (GND) maintained and used cooperatively by many libraries in German-speaking countries and the United States Library of Congress. The idea is to create a single worldwide virtual authority file. For example, the ID for Princess Diana in the GND is 118525123 (preferred name: Diana < Wales, Prinzessin>) while the United States Library of Congress uses the term Diana, Princess of Wales, 1961–1997; other authority files have other choices. The Virtual International Authority File choice for all of these variations is VIAF ID: 107032638 — that is, a common number representing all of these variations.
The English Wikipedia prefers the term "Diana, Princess of Wales", but at the bottom of the article about her, there are links to various international cataloging efforts for reference purposes.
=== Same name describes two different subjects ===
Sometimes two different authors have been published under the same name. This can happen if there is a title which is identical to another title or to a collective uniform title. This, too, can cause confusion. Different authors can be distinguished correctly from each other by, for example, adding a middle initial to one of the names; in addition, other information can be added to one entry to clarify the subject, such as birth year, death year, range of active years such as 1918–1965 when the person flourished, or a brief descriptive epithet. When catalogers come across different subjects with similar or identical headings, they can disambiguate them using authority control.
== Authority records and files ==
A customary way of enforcing authority control in a bibliographic catalog is to set up a separate index of authority records, which relates to and governs the headings used in the main catalog. This separate index is often referred to as an "authority file". It contains an indexable record of all decisions made by catalogers in a given library (or—as is increasingly the case—cataloging consortium), which catalogers consult when making, or revising, decisions about headings. As a result, the records contain documentation about sources used to establish a particular preferred heading, and may contain information discovered while researching the heading which may be useful.
While authority files provide information about a particular subject, their primary function is not to provide information but to organize it. They contain enough information to establish that a given author or title is unique, but that is all; irrelevant but interesting information is generally excluded. Although practices vary internationally, authority records in the English-speaking world generally contain the following information:
Headings show the preferred title chosen as the official and authorized version. It is important that the heading be unique; if there is a conflict with an identical heading, then one of the two will have to be chosen:Since the headings function as access points, making sure that they are distinct and not in conflict with existing entries is important. For example, the English novelist William Collins (1824–89), whose works include the Moonstone and The Woman in White is better known as Wilkie Collins. Cataloguers [sic] have to decide which name the public would most likely look under, and whether to use a see also reference to link alternative forms of an individual's name.
Cross references are other forms of the name or title that might appear in the catalog and include:
see references are forms of the name or title that describe the subject but which have been passed over or deprecated in favor of the authorized heading form
see also references point to other forms of the name or title that are also authorized. These see also references generally point to earlier or later forms of a name or title.
Statement(s) of justification is a brief account made by the cataloger about particular information sources used to determine both authorized and deprecated forms. Sometimes this means citing the title and publication date of the source, the location of the name or title on that source, and the form in which it appears on that source.

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For example, the Irish writer Brian O'Nolan, who lived from 1911 to 1966, wrote under many pen names such as Flann O'Brien and Myles na Gopaleen. Catalogers at the United States Library of Congress chose one form—"O'Brien, Flann, 1911–1966"—as the official heading. The example contains all three elements of a valid authority record: the first heading O'Brien, Flann, 1911–1966 is the form of the name that the Library of Congress chose as authoritative. In theory, every record in the catalog that represents a work by this author should have this form of the name as its author heading. What follows immediately below the heading beginning with Na Gopaleen, Myles, 1911–1966 are the see references. These forms of the author's name will appear in the catalog, but only as transcriptions and not as headings. If a user queries the catalog under one of these variant forms of the author's name, he or she would receive the response: "See O'Brien, Flann, 1911–1966." There is an additional spelling variant of the Gopaleen name: "Na gCopaleen, Myles, 1911–1966" has an extra C inserted because the author also employed the non-anglicized Irish spelling of his pen-name, in which the capitalized C shows the correct root word while the preceding g indicates its pronunciation in context. So if a library user comes across this spelling variant, he or she will be led to the same author regardless. See also references, which point from one authorized heading to another authorized heading, are exceedingly rare for personal name authority records, although they often appear in name authority records for corporate bodies. The final four entries in this record beginning with His At Swim-Two-Birds ... 1939. constitute the justification for this particular form of the name: it appeared in this form on the 1939 edition of the author's novel At Swim-Two-Birds, whereas the author's other noms de plume appeared on later publications.
== Access control ==
The act of choosing a single authorized heading to represent all forms of a name is quite often a difficult and complex task, considering that any given individual may have legally changed their name or used a variety of legal names in the course of their lifetime, as well as a variety of nicknames, pen names, stage names or other alternative names. It may be particularly difficult to choose a single authorized heading for individuals whose various names have controversial political or social connotations, when the choice of authorized heading may be seen as endorsement of the associated political or social ideology.
An alternative to using authorized headings is the idea of access control, where various forms of a name are related without the endorsement of one particular form.
== Cooperative cataloging ==
Before the advent of digital online public access catalogs and the Internet, individual cataloging departments within each library generally carried out creating and maintaining a library's authority files. Naturally, there was a considerable difference in the authority files of the different libraries. For the early part of library history, it was generally accepted that, as long as a library's catalog was internally consistent, the differences between catalogs in different libraries did not matter greatly.
As libraries became more attuned to the needs of researchers and began interacting more with other libraries, the value of standard cataloging practices came to be recognized. With the advent of automated database technologies, catalogers began to establish cooperative consortia, such as OCLC and RLIN in the United States, in which cataloging departments from libraries all over the world contributed their records to, and took their records from, a shared database. This development prompted the need for national standards for authority work.
In the United States, the primary organization for maintaining cataloging standards with respect to authority work operates under the aegis of the Library of Congress Program for Cooperative Cataloging. It is known as the Name Authority Cooperative Program, or NACO Authority.
== Standards ==
There are various standards using different acronyms.
=== Standards for authority metadata ===
MARC standards for authority records in machine-readable format.
Metadata Authority Description Schema (MADS), an XML schema for an authority element set that may be used to provide metadata about agents (people, organizations), events, and terms (topics, geographics, genres, etc.).
Encoded Archival Context, an XML schema for authority records conforming to ISAAR.
=== Standards for object identification, controlled by an identification-authority ===
Legal personality identification systems (person-IDs) and authorities:
serey
(CPF) – International Standard Archival Authority Record for Corporate Bodies, Persons, and Families. Published by the International Council on Archives
ISNI – International Standard Name Identifier
ORCID – Open Researcher and Contributor ID, a subset of the ISNI, to uniquely identify scientific and other academic authors.
DAI – Digital Author Identification, another subset of ISNI.
GRID – Global Research Identifier Database
GND – Integrated Authority File (Gemeinsame Normdatei), authority file for personal names, corporate bodies and subject headings.
KANTO – National Agent Data (finaf), authority file for persons and corporate bodies.
LCCN – Library of Congress Control Number
NDL – National Diet Library
VIAF – Virtual International Authority File, an aggregation of authority files currently focused on personal and corporate names.
WorldCat/identities
Bibliographic object identification systems and authorities:
DOI – Digital object identifier
urn:lex, for law-document identifiers, controlled by local law authorities.
ISBN – International Standard Book Number
ISSN – International Standard Serial Number
Other identification systems (for generic named-entities) and authorities:
GeoNames
TGN – Getty Thesaurus of Geographic Names
=== Standards for identified-object metadata ===
vCard
Dublin Core
== See also ==
Persistent identifier
Knowledge Organization Systems
Library classification systems:
Dewey Decimal Classification
Library of Congress Classification
Ontology (information science)
Proprietary services
ResearcherID
Registration authority
Simple Knowledge Organization System (SKOS)
== References ==

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Bibliomining is the use of a combination of data mining, data warehousing, and bibliometrics for the purpose of analyzing library services. The term was created in 2003 by Scott Nicholson, Assistant Professor, Syracuse University School of Information Studies, in order to distinguish data mining in a library setting from other types of data mining.
== How bibliomining works ==
First a data warehouse must be created. This is done by compiling information on the resources, such as titles and authors, subject headings, and descriptions of the collections. Then the demographic surrogate information is organized. Finally the library information (such as the librarian, whether or not the information came from the reference desk or circulation desk, and the location of the library) is obtained.
Once this is organized, the data can be processed and analyzed. This can be done via a few methods, such as online analytical processing (OLAP), using a data mining program, or through data visualization.
== Uses of bibliomining ==
Bibliomining is used to discover patterns in what people are reading and researching and allows librarians to target their community better. Bibliomining can also help library directors focus their budgets on resources that will be utilized. Another use is to determine when people use the library more often, so staffing needs can be adequately met. Combining bibliomining with other research techniques such as focus groups, surveys and cost-benefit analysis, will help librarians to get a better picture of their patrons and their needs.
== Issues ==
There is some concern that data mining violates patron privacy. But by extracting the data, all personally identifiable information is deleted, and the data warehouse is clean. The original patron data can then be totally deleted and there will be no way to link the new data to a particular patron. This can be done in a few ways. One, used with information regarding database access, is to track the IP address, but then replace it with a similar code, that will allow identification without violating privacy. Another is to keep track of an item returned to the library and create a "demographic surrogate" of the patron. The demographic surrogate would not give any identifiable information such as names, library card numbers or addresses.
The other concern in bibliomining is that it only provides data in a very detached manner. Information is given as to how a patron uses library resources, but there is no way to track if the resources met the user's needs completely. Someone could take out a book on a topic, but not find the information they were seeking. Bibliomining only helps identify which books are used, not how useful they actually were. Bibliomining cannot provide information on how well a collection serves a patron. In order to counteract this, bibliomining must be used in accordance with other research techniques.
== See also ==
Iris.AI
== References ==
== Further reading ==

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The term born-digital refers to materials that originate in a digital form. This is in contrast to digital reformatting, through which analog materials become digital, as in the case of files created by scanning physical paper records. It is most often used in relation to digital libraries and the issues that go along with said organizations, such as digital preservation and intellectual property. However, as technologies have advanced and spread, the concept of being born-digital has also been discussed in relation to personal consumer-based sectors, with the rise of e-books and evolving digital music. Other terms that might be encountered as synonymous include "natively digital", "digital-first", and "digital-exclusive".
== Discrepancies in definition ==
There exists some inconsistency in defining born-digital materials. Some believe such materials must exist in digital form exclusively; in other words, if they can be transferred into a physical, analog form, they are not truly born-digital. However, others maintain that while these materials will often not have a subsequent physical counterpart, having one does not bar them from being classified as 'born-digital'. For instance, Mahesh and Mittal identify two types of born-digital content, "exclusive digital" and "digital for print", allowing for a broader base of classification than the former definition provides.
Furthermore, it has been pointed out that certain works may incorporate components that are both born-digital and digitized, further blurring the lines between what should and should not be considered 'born-digital.' For example, a digital video created may utilize historical film footage that has been converted. It is important to be aware of these discrepancies when thinking about born-digital materials and the effects they have. However, some universals do exist across these definitions. All make clear the fact that born-digital media must originate digitally. Also, they agree that this media must be able to be utilized in a digital form (whether exclusively or otherwise), while they do not have to exist or be used as analog materials.
== Etymology ==
The term "born digital" is of uncertain origin. While it may have occurred to multiple people at various times, it was coined independently by web developer Randel (Rafi) Metz in 1993, who acquired the domain name "borndigital.com" then and sustained it as a personal website for 18 years until 2011. The domain is now owned by a web developer in New Zealand. The original website is archived here.
== Examples of born-digital content ==
=== Grey literature and communications ===
Much of the grey literature that exists today are almost entirely conducted online, due in part to the accessibility and speed of internet communications. As the products of the vast amount of information created by organizations and individuals on computers, data sets and electronic records must exist in the context of other activities. Common content includes:
Email
Documents created in word processors and/or observed in viewers. Examples include Microsoft Word, Google Docs, WordPerfect, Apple Pages, LibreOffice Writer, and Adobe Reader.
Spreadsheets used to organize and tabulate data are almost entirely digital. Common applications include Microsoft Excel, Google Sheets, LibreOffice Calc, and Lotus 1-2-3 (discontinued).
Presentations used to present data and ideas are created with software such as Microsoft PowerPoint, Google Slides, LibreOffice Impress, and Prezi.
Electronic medical records
Social media websites such as Facebook, Twitter, and Reddit have originated in the networked world, and are therefore born-digital by default.
==== Digital photography ====
Digital photography has allowed larger groups of people to participate in the process, art form, and pastime of photography. With the advent of digital cameras in the late 1980s, followed by the invention and dissemination of mobile phones capable of photography, sales of digital cameras eventually surpassed that of analog cameras. The early to mid 2000s saw the rise of photo storage websites, such as Flickr and Photobucket, and social media websites dedicated primarily to sharing digital photographs, including Instagram, Pinterest, Imgur, and Tumblr. Digital image files include Joint Photographic Experts Group (JPEG), Tagged Image File Format (TIFF), Portable Network Graphics (PNG), Graphic Interchange Format (GIF), and raw image format.
==== Digital art ====
Digital art is an umbrella term for art created with a computer. Types include visual media, digital animation, computer-aided design, 3D models and interactive art. Webcomics, comics published primarily on the internet, are an example of exclusively born-digital art. Webcomics follow the tradition of user-generated content and may later be printed by the creator, but as they were originally disseminated through the internet, they are considered to be born-digital media. Many webcomics are published on existing social media websites, while others use webcomic-specific platforms, such as Webtoon, or their own domains.
==== Electronic books ====
E-books are books that can be read through the digital screens of computers, smartphones, or dedicated devices. The e-book sector of the book industry has flourished in recent years, with increasing numbers of e-books and e-book readers being developed and sold. E-publishing is particularly favorable to independent authors, because the digital marketplace creates a more direct connection between authors, their works, and the audience. Some publishing houses, including major ones such as Harlequin, have formed imprints for digital-only books in response to this trend. Publishers also offer digital-exclusive publications for use on e-book readers, such as the Kindle. One example of this was with the simultaneous launch of Amazon's Kindle 2 with the Stephen King novelette Ur. In recent years, however, the sale of e-books from traditional publishers has decreased, due in part to increasing prices.
==== Video recordings ====
Videos that are born-digital vary in type and usage. Vlogs, an amalgamation of "video" and "blog," are streamed and consumed on video-sharing websites such as YouTube.
Similarly, a web series is a television-like show that is shown exclusively and/or initially on the internet. This does not include the streaming of pre-existing traditional television shows. Examples include Dr. Horrible's Sing Along Blog, The Lizzie Bennett Diaries, The Guild, and The Twilight Zone (2019).

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==== Sound recordings ====
Digital sound recordings have played a role since the 1970s with the acceptance of pulse-code modulation (PCM) in the recording process. Since then, numerous means of storing and delivering digital audio have been developed, including web streams, compact discs and mp3 audio files. Increasingly, digital audio are only available via download, lacking any kind of tangible counterpart. One example of this trend is the 2008 recording of Hector Berlioz's Symphonie fantastique by Los Angeles Philharmonic under Gustavo Dudamel. Available through download only, it has presented problems for libraries which may want to carry this work but cannot due to licensing limitations. Another example is Radiohead's 2007 release In Rainbows, released initially as a digital download, before later receiving a physical release.
==== Other media ====
WebExhibits are websites that act as virtual museums for any variety of content. These often use both primary and secondary historical sources, maps, timelines, infographics, and other data visualizations to showcase the historical past. One example is Clio Visualizing History's Click! The Ongoing Feminist Revolution, a web exhibit about the American women's movement from the 1940s to the present. Clio Visualizing History was founded by Lola Van Wagenen in 1996 to meet the growing need for innovative history projects in multi-media platforms.
=== Journalism ===
As existing print publications migrated to born-digital releases, digital native news websites such as HuffPo and Buzzfeed News have grown substantially. This trend toward web-exclusive content has seen the rise of "news applications," or news articles built with interactive features that cannot be replicated on print. "News Apps" are often heavily data-driven, using interactive graphics custom-built for the story by a team of software specialists in addition to the core group of writers and editors. Examples include Baltimore Homicides from The Baltimore Sun, Do No Harm from the Las Vegas Sun, and Snow Fall from The New York Times, which took a team of more than fifteen journalists, web developers, and designers to build.
== Key issues ==
=== Preservation ===
Digital preservation involves the conservation and maintenance of digital content. As with other digital objects, preservation must be a continuous and regular undertaking, as these materials do not show the same signs of degradation that print and other physical materials do. Invisible processes such as bit rot can lead to irreparable damage. In the case of born-digital content, deterioration can occur in the form of bit rot, a process in which digital files degrade over time, and link rot, a process in which URLs link to pages on the internet that are no longer available. Incompatibility is also a concern, in regard to the eventual obsolescence of both hardware and software capable of making sense of the documents.
Many questions arise regarding what should be archived and preserved and who should undertake the job. Vast amounts of born-digital content are created constantly and institutions are forced to decide what and how much should be saved. Because linking plays such a large role in the digital setting, whether a responsibility exists to maintain access to links (and therefore context) is debated, especially when considering the scope of such a task. Additionally, since publishing is not as delineated in the digital realm and preliminary versions of work are increasingly made available, knowing when to archive presents further complications.
=== Relevance and accessibility ===
For digital libraries and repositories that are used as reference materials, such as PBS LearningMedia, which provides educational resources for teachers, staying relevance is of utmost importance. The information must be factually accurate and include context, while staying current to the website's main goals. As in the case of preservation, bit rot, link rot, and incompatibility negatively affect how users might access born-digital records, while mere functionality, e.g. video quality and legibility of any text, is also a concern. Additionally, considerations on how digital content can be inclusive of people with disabilities should be made, particularly in conjunction with assistive technologies such as screen readers, screen magnifiers, and speech-to-text software. Access is also affected by licensing laws — the lack of ownership of their digital collections leaves libraries with nothing when their license expires, despite the costs already paid.

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=== Licensing ===
Laws created to protect the intellectual property were written for analog works; as such, provisions such as the first-sale doctrine of US copyright law, which enables libraries to lend materials to patrons, have not been applied to the digital realm. Therefore, certain copyrighted digital content that is licensed rather than owned, as is common with many digital materials, is often of limited use since it cannot be transmitted to patrons at various computers or lent through an interloan agreement. However, with regards to the preservation functions of libraries and archives and the subsequent need to make copies of born-digital materials, the laws of many countries have been changing, allowing for agreements to be made between these institutions and the rights holders of born-digital content.
Consumers have also had to deal with intellectual property as it concerns their ownership of and ability to control the born-digital material that they buy. Piracy proves to be a bigger problem with digital objects, including those that are born-digital, because such materials can be copied and spread in perfect condition with speed and distance on a scale inconceivable for traditional print and physical materials. Again, the first-sale doctrine, which, from a consumer standpoint, allows purchasers of materials to sell or give away items (such as books and CDs), is not yet applied effectively to digital objects. Three reasons for this have been identified by Victor Calaba: "...first, license agreements imposed by software manufacturers typically prohibit exercise of the first sale doctrine; second, traditional copyright law may not support application of the first sale doctrine to digital works; finally, the Digital Millennium Copyright Act functionally prevents users from making copies of digitized works and prohibits the necessary bypassing of access control mechanisms to facilitate a transfer."
Increasingly, institutions are more interested in subscribing to digital versions of journals, something observed as some scholarly journals have unbundled their print and electronic editions and allowed for separate subscription; these trends have created questions about the economic sustainability of print publication. Major journals such as the American Chemical Society have made significant changes to their print editions in order to cut costs, and many others predict an exclusively digital future. The increasing subscription prices and predatory practices of scholarly journals, however, provided impetus for the Open Access Movement, which advocates for free, unrestricted access to scholarly papers.
== See also ==
e-Flux
Digital artifactual value
Digital curation
Legal deposit
National edeposit, Australia's system for depositing, storing and managing all born-digital documents published in Australia
Virtual artifact
== References ==

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Butts and bounds, shortened form for "abuttals and boundaries" of a property, are the boundary lines delineated between plots of land, usually those which define the end of an estate, as used in legal deeds, titles, etc. These are usually descriptive features in the property, such as trees, outcroppings of stone, or riverine brooks, etc., and are signified in the legal deed for purposes of identification.
== Historical uses ==
The practice of signifying butts and bounds in the sale of real estate and in legal deeds and contracts is an ancient practice, having attestation in the Hebrew Bible. In the episode of Abraham who purchased the field of Ephron in Genesis 23:17, and where it describes the cave and the trees in the outermost bounds of the property, the Sages of Israel learnt thereby that he that sells his field must write in the deed its landmarks and boundaries.
According to rabbinic tradition, Joshua, when dividing the Land of Canaan among the twelve tribes of Israel, planted Sea squill (Hebrew: חצוב) to mark off the butts and bounds of tribal inheritance. The practice was still prevalent along the coast of the Syrian-Egyptian desert as late as the 20th-century.
In Jewish laws of agronomy, the prohibition of marking off butts and bounds beginning on the first day of the lunar month Tishri during the Seventh-year (until the end of that year) is expressly stated in the compendium of Jewish oral law known as the Mishnah (Shevi'it 2:2):
Until the New Year they may mark the butts and bounds of property (Hebrew: מיבלין), strip off leaves, cover up [exposed] roots or fumigate plants.
=== Legal deeds of conveyance ===
The civil laws with respect to standard formularies used in drafting documents and legal deeds differ from country to country. For example, in some societies the custom requires that, where there are no distinct physical features in the said property, it is sufficient to mention the name(s) of the property owner(s) of the adjacent fields. As early as anno 500 CE it was litigated:
If the field is bounded by fields of Reuben on the east and west and by fields of Simeon on the north and south, he must write, 'the field is bounded by fields of Reuben on two sides, and by fields of Simeon on two sides.' [And not simply, 'It lies between the fields of Reuben and Simeon,' which leaves room for ambiguity.]
In older legal deeds, the phrase "butted and bounded by..." often precedes the actual description of the ends of the land in question. In modern conveyances of real estate, the legal term is often defined as Parcels clause.
=== USA ===
With the development of modern surveying techniques in Europe and the proposals put forward before the US Congress under the Land Ordinance of 1785, a more efficient way was devised in the United States for the layout, sale and disposal of private and public lands, known as the Public Land Survey System. This new system formed the basis for dividing all territory, and where it called-out unto surveyors in their respective places to take an account of all lands, and to divide the same territory into Townships of six miles square, by lines running due north and south, and others crossing these at right angles. The plats of townships respectively were to be marked by subdivisions consisting each of lots of one mile square, or 640 acres, and numbered from 1 to 36. These numbered subdivisions were known as Sections. Sections could also be divided into four equal quarters (fractions of a section), known simply as NW [= north-west], NE [= north-east], SW [= south-west] and SE [= south-east], while each quarter could be subdivided into another four quarters, such that the north-east quarter when divided into four more quarters, would have the designation of either SENE [= south-east of North-east quarter], or SWNE [= south-west of North-east quarter], or NWNE (north-west of North-east quarter], or NENE [= north-east of North-east quarter]. In this manner, all sections were duly divided. Thus, by this means, land holders who either bought land or who were granted land due to their military service, were able to register their holdings in their names, in their respective counties, with the date of purchase or issuance of a military warrant, and the precise location of the property (e.g. lands of Section 14, in Township 11S [= eleven South], of Range 14W [= fourteen West]) ascribed to the person. Township numbers were always followed by a principal meridian directional sign (either N or S [= for north and south]), while the range number was always followed by a base line directional sign (either E or W [= for east and west]).
=== Australia ===
In Australian common law, which shares a common law heritage with the United Kingdom, Canada and the United-States, "A description by abuttals will, as a rule, override measurements expressed in figures if conflict exists between description and measurement". The same rule applies in 2nd-century Judaic law, except where the seller had noted in the transaction that he was selling to the buyer a parcel of land defined by measurement, and which same measurement he (the seller) expressly stated as extending as far as its physical butts and bounds. Had the buyer discovered, when he came to take an account of his field, that the butts and bounds did not extend so far, but were one-sixth (1⁄6) less than the designated measurement avouched by the seller, the sale does not hold-up as good, seeing that the conditions were fraudulent, in which case, the seller is required to reimburse to its buyer the difference paid (diminishing one-sixth of the cost), or else give to him more land. When both measurement and descriptive features are used, anything less than a deviancy of 1⁄6 is still in the realm of accuracy.
== Historical example ==
The following deed of sale from the US shows the parameters of a plot of land, bounded by trees and a river:
== See also ==
Beating of the bounds
Boundary (real estate)
Boundary marker
Deed
Land lot
Metes and bounds
Title (property)
== References ==
== External links ==
Christopher Fennell, "An Account of James Monroe's Land Holdings: Surveying terminology"

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Chronostratigraphy is the branch of stratigraphy that studies the ages of rock strata in relation to time.
The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of the Earth.
The standard stratigraphic nomenclature is a chronostratigraphic system based on palaeontological intervals of time defined by recognised fossil assemblages (biostratigraphy). The aim of chronostratigraphy is to give a meaningful age date to these fossil assemblage intervals and interfaces.
== Methodology ==
Chronostratigraphy relies heavily upon isotope geology and geochronology to derive hard dating of known and well defined rock units which contain the specific fossil assemblages defined by the stratigraphic system. In practice, as it is very difficult to isotopically date most fossils and sedimentary rocks directly, inferences must be made in order to arrive at an age date which reflects the beginning of the interval.
The methodology used is derived from the law of superposition and the principles of cross-cutting relationships.
Because igneous rocks occur at specific intervals in time and are essentially instantaneous on a geologic time scale, and because they contain mineral assemblages which may be dated more accurately and precisely by isotopic methods, the construction of a chronostratigraphic column relies heavily upon intrusive and extrusive igneous rocks.
Metamorphism, often associated with faulting, may also be used to bracket depositional intervals in a chronostratigraphic column. Metamorphic rocks can occasionally be dated, and this may give some limitations to the age in which a bed could have been laid down. For example, if a bed containing graptolites overlies crystalline basement at some point, dating the crystalline basement will give a maximum age of that fossil assemblage.
This process requires a considerable degree of effort and checking of field relationships and age dates. For instance, there may be many millions of years between a bed being laid down and an intrusive rock cutting it; the estimate of age must necessarily be between the oldest cross-cutting intrusive rock in the fossil assemblage and the youngest rock upon which the fossil assemblage rests.
== Units ==
Chronostratigraphic units, with examples:
eonothem – Phanerozoic
erathem – Paleozoic
system – Ordovician
series – Upper Ordovician
stage – Ashgill
== Differences from geochronology ==
It is important not to confuse geochronologic and chronostratigraphic units. Chronostratigraphic units are geological material, so it is correct to say that fossils of the species Tyrannosaurus rex have been found in the Upper Cretaceous Series. Geochronological units are periods of time and take the same name as standard stratigraphic units but replacing the terms upper/lower with late/early. Thus it is also correct to say that Tyrannosaurus rex lived during the Late Cretaceous Epoch.
Chronostratigraphy is an important branch of stratigraphy because the age correlations derived are crucial in drawing accurate cross sections of the spatial organization of rocks and in preparing accurate paleogeographic reconstructions.
== See also ==
Biostratigraphy
Chronozone
Geochronology
Geologic record
Geologic time scale
List of geochronologic names
Tectonostratigraphy
== References ==

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A chronozone or chron is a unit in chronostratigraphy, defined by events such as
geomagnetic reversals (magnetozones), or based on the presence of specific fossils (biozone or biochronozone).
According to the International Commission on Stratigraphy, the term "chronozone" refers to the rocks formed during a particular time period, while "chron" refers to that time period.
Although non-hierarchical, chronozones have been recognized as useful markers or benchmarks of time in the rock record. Chronozones are non-hierarchical in that chronozones do not need to correspond across geographic or geologic boundaries, nor be equal in length. Although a former, early constraint required that a chronozone be defined as smaller than a geological stage. Another early use was hierarchical in that Harland et al. (1989) used "chronozone" for the slice of time smaller than a faunal stage defined in biostratigraphy.
The ICS superseded these earlier usages in 1994.
The key factor in designating an internationally acceptable chronozone is whether the overall fossil column is clear, unambiguous, and widespread. Some accepted chronozones contain others, and certain larger chronozones have been designated which span whole defined geological time units, both large and small.
For example, the chronozone Pliocene is a subset of the chronozone Neogene, and the chronozone Pleistocene is a subset of the chronozone Quaternary.
== See also ==
Body form
Chronology (geology)
European Mammal Neogene
Geologic time scale
North American Land Mammal Age
Type locality (geology)
List of GSSPs
== References ==
== External links ==
International Stratigraphic Chart from the International Commission on Stratigraphy
USA National Park Service
Washington State University Archived 2011-07-26 at the Wayback Machine
Web Geological Time Machine
Eon or Aeon, Math Words - An alphabetical index
The Global Boundary Stratotype Section and Point (GSSP): overview
Chart of The Global Boundary Stratotype Sections and Points (GSSP): chart
Geotime chart displaying geologic time periods compared to the fossil record

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Claim clubs, also called actual settlers' associations or squatters' clubs, were a nineteenth-century phenomenon in the American West. Usually operating within a confined local jurisdiction, these pseudo-governmental entities sought to regulate land sales in places where there was little or no legal apparatus to deal with land-related quarrels of any size. Some claim clubs sought to protect squatters, while others defended early land owners. In the twentieth century, sociologists suggested that claim clubs were a pioneer adaptation of democratic bodies on the East Coast, including town halls.
== Purpose ==
Claim clubs were essentially designed to "do what politicians refused to do: make land available to needy settlers." Their general purpose was to protect the first settlers to arrive on unclaimed lands, particularly in their rights to speculate and cultivate. With the continuous availability of frontier lands from the 1830s through the 1890s, settlers kept moving west. Each claim club established its own rules of governance and enforcement; however, these were almost always vigilante actions. Period accounts report that in some areas, claim clubs were regarded with "the same majesty of the law of the Supreme Court of the United States."
East Coast land speculators were prone to roam the recently opened Western United States and select the most desirable spots with the intent to outbid the settler and real claimant when the lands were offered for sale at the Land Office. Claim jumpers were also a problem. Generally they sought to be present at a land sale when the first claimant was not there. In many cases, when people who claimed land and then did not live on it and had not developed it with a shelter, fencing or other structures, "claim jumpers" would move in.
This was one scenario where claim clubs would enter. The absentee-owned land would be exploited directly and indirectly, or just simply seized with the title held "by claim club." Members might vote expensive local improvements for the land, including roads and schoolhouses, and assign the heavy costs of development as a tax burden on the land held by absentees. This became the regular policy of some claim clubs, designed to force the sale by absentee owners to actual residents, or at least to local speculators.
Claim clubs did not always protect the honest settler against the scheming speculator. Although claim club law sometimes shielded of the simple homesteader, it was also a tool and a weapon of the speculator. Claim clubs acted not only to protect a squatter's title to land he lived on and was cultivating, but also to help the same squatter defend unoccupied second and third tracts against the claim of later arrivals.
The institution of the claim club is said to have "reached perfection" in Iowa, where more than a hundred such groups carefully regulated land commerce until the United States government intervened.
== Examples ==
One early claim club in the United States was established by settlers around Burlington, Iowa, where claims were formed before the Sauk and Meskwaki peoples ceded the area in 1832. These clubs were established in direct violation of federal law, in what J. Sterling Morton described as a claim meeting. According to one report, "Such clubs sprang up 'as readily as did the sunflowers wherever the prairie sod was broken' in Illinois, Wisconsin, Iowa, Minnesota, Nebraska..." Other reports corroborate the spread of claim clubs, with their presence felt in the aforementioned states, as well as New Mexico, North Dakota, Wyoming, Montana, Colorado and Washington.
=== Colorado ===
In Old Colorado City, Colorado, the El Paso Claim Club was formed by members of the Colorado City Town Company in 1859. The Club reportedly "settled land disputes and recorded real property transactions until federal government regulations provided for an official land office in 1862."
The Cañon City (Colorado) Claim Club first platted the town of Cañon City in 1860. The club had six members, each of whom mined coal, iron, gypsum, marble and granite mining in the area, and Denver also had a claim club.
=== Nebraska ===
The Omaha Claim Club was founded in 1854, the year the city was founded. Initially designed to protect the interests of 20 men, it grew to include almost two hundred settlers. The group used violent means to impose "frontier justice", including dunking in the frozen Missouri River, running off legitimate settlers, and other forms of vigilantism. The club imposed their will on the Nebraska Territorial Legislature as well, and with the passage of a territorial law granting 320 acres (1.3 km2) per settler, they doubled the federally imposed limit of 160 acres (0.6 km2). The club ran Omaha until the Supreme Court ruled against their violent measures in Baker v. Morton, a hallmark in contract law cases.
In the 1854 the Bellevue (Nebraska) Claim Club was organized. The original aim of the club was "to secure the peaceful adjustment of all cases in which claims in this then un-surveyed country overlapped each other." The club was renowned for visiting "claim jumpers" with beatings to convince them to leave their claims. Its last act, reportedly in 1858, was to attempt to tar and feather an old man and his three sons reportedly squatting in the area. The Platte Valley Claim Club was established in Fremont in August, 1856 to settle land disputes, and folded by late 1857.
Fort Saint Vrain, Nebraska Territory also had a claim club in the late 1850s that was designed to keep the town from failing. It did not succeed.

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=== Kansas ===
One story of claim club "justice" comes from Montgomery County, Kansas town in 1867. An early settler had tilled his land and improved on it, according to the provisions of the Homestead Act. However, he had not lived on it for five years. After he sold it to another man, this same settler reportedly went to the United States Land Office to preempt the man to whom he sold the land. After doing so this settler attempted to displace the man he sold the land to and claim it as his own. When the local claim club ordered the town sheriff to "put the man away", the original settler was never seen again.
=== Iowa ===
Claim clubs also secured members' stakes on land they speculated to become important to the federal government, for the purpose of selling it back to the government at a later date. Members of one Iowa claim club purchased 15,000 acres (61 km2) in central Iowa, which eventually was sold in order to develop both the state capitol in Des Moines and Iowa City, where the state university is today.
Iowa had several other claim clubs, as well. In Fort Des Moines, Fort Dodge, Iowa and Iowa City active clubs abounded. In Iowa City the club's mission was to "...protect all persons who do or may hold claims, against the interference of any person who shall attempt to deprive such claim holders of their claims and improvements, by preemption or otherwise."
=== Others ===
From 1832 to 1843, Dupage County, Illinois created a number of claim clubs until the federal land surveyors arrived. In 1835 settlers in Elkhorn Creek, Wisconsin formed a claim club. Other settlers did the same, including the town of Yankton, South Dakota. There is also a report of a claim club in Alabama in the 1850s.
== Decline ==
In the latter part of the 1850s claim clubs came under pressure from the federal government, and lost public support in many communities. In an 1858 ruling, the United States Department of the Interior addressed claim clubs directly, stating that, "A member of a claim club, organized for the purpose of illegally appropriating and selling public lands, will be held to the strictest proof of honest intent, when asserting an individual claim."
The violent actions of the Omaha Claim Club may have brought about the demise of claim clubs across the country. In 1860, in Baker v. Morton, the Supreme Court ordered that city's club to disband. Other sources say that with the arrival of several United States Land Offices across the West, the claim clubs simply were not needed.
The Omaha Claim Club, along with many claim clubs around Nebraska, disbanded by 1860.
== See also ==
Preemption Act of September 4, 1841
Bald Knobbers
Stockgrowers association
== References ==

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In physical geography, a dell is a grassy hollow—or dried stream bed—often partially covered in trees. In literature, dells have pastoral connotations, frequently imagined as secluded and pleasant safe havens.
The word "dell" comes from the Old English word dell, which is related to the Old English word dæl, modern 'dale'. The term is sometimes used interchangeably with the word "dingle", although "dingle" specifically refers to deep ravines or hollows that are embowered with trees. The terms have also been combined to form examples of tautological placenames in Dingle Dell, Kent, and Dingle Dell Reserve, Auckland.
== In popular culture ==
Rivendell – Fictional valley of Elves in J. R. R. Tolkien's Middle-earth — Tolkien's fictional Elvish locale.
Derndingle — in The Lord of the Rings, the place in Fangorn Forest where the Entmoot is held.
"The Farmer in the Dell" – an American folk song brought to United States by German immigrants.
"This Lime-Tree Bower My Prison" - A poem by Samuel Taylor Coleridge, makes reference to a dell in lines 5-10.
== Related places ==
Hollywood Dell, Los Angeles
Hollywood Bowl – Amphitheater in Los Angeles, California
Matthiessen State Park – State park in Illinois, US
Wisconsin Dells – Gorge on the Wisconsin River in Wisconsin, United States
The Dell (Wellington, New Zealand) – A flat, sheltered lawn area with a stage, surrounded by steep hills
== See also ==
Cirque – Amphitheatre-like valley formed by glacial erosion
Coulee – Type of valley or drainage zone
Glen – Name for valley commonly used in Ireland, Scotland and the Isle of Man
U-shaped valley, also known as glaciated valley – Valleys formed by glacial scouring
Gully – Landform created by running water and/or mass movement eroding sharply into soil
Canyon, also known as Gorge – Deep chasm between cliffs
Valley – Low area between hills, often with a river running through it
== References ==
== External links ==
Media related to Dells at Wikimedia Commons

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A depocenter or depocentre in geology is the part of a sedimentary basin where a particular rock unit has its maximum thickness. Depending on the controls on subsidence and the sedimentary environment, the location of a basin's depocenter may vary with time, such as in active rift basins as extensional faults grow, link or become abandoned.
== References ==

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Discoverability is the degree to which something, especially a piece of content or information, can be found in a search of a file, database, or other information system. Discoverability is a concern in library and information science, many aspects of digital media, software and web development, and in marketing, since products and services cannot be used if people cannot find it or do not understand what it can be used for.
Metadata, or "information about information", such as a book's title, a product's description, or a website's keywords, affects how discoverable something is on a database or online. Adding metadata to a product that is available online can make it easier for end users to find the product. For example, if a song file is made available online, making the title, band name, genre, year of release, and other pertinent information available in connection with this song means the file can be retrieved more easily. The organization of information through the implementation of alphabetical structures or the integration of content into search engines exemplifies strategies employed to enhance the discoverability of information.
The concept of discoverability, while related to but distinct from accessibility and usability, which are other qualities that affect the usefulness of a piece of information, is a critical aspect of information retrieval.
== Etymology ==
The concept of "discoverability" in an information science and online context is a loose borrowing from the concept of the similar name in the legal profession. In law, "discovery" is a pre-trial procedure in a lawsuit in which each party, through the law of civil procedure, can obtain evidence from the other party or parties by means of discovery devices such as a request for answers to interrogatories, request for production of documents, request for admissions and depositions. Discovery can be obtained from non-parties using subpoenas. When a discovery request is objected to, the requesting party may seek the assistance of the court by filing a motion to compel discovery.
== Purpose ==
The usability of any piece of information directly relates to how discoverable it is, either in a "walled garden" database or on the open Internet. The quality of information available on this database or on the Internet depends upon the quality of the meta-information about each item, product, or service. In the case of a service, because of the emphasis placed on service reusability, opportunities should exist for reuse of this service. However, reuse is only possible if information is discoverable in the first place. To make items, products, and services discoverable, the process is as follows:
Document the information about the item, product or service (the metadata) in a consistent manner.
Store the documented information (metadata) in a searchable repository.
while technically a human-searchable repository, such as a printed paper list would qualify, "searchable repository" is usually taken to mean a computer-searchable repository, such as a database that a human user can search using some type of search engine or "find" feature.
Enable search for the documented information in an efficient manner.
supports number 2, because while reading through a printed paper list by hand might be feasible in a theoretical sense, it is not time and cost-efficient in comparison with computer-based searching.
Apart from increasing the reuse potential of the services, discoverability is also required to avoid development of solution logic that is already contained in an existing service. To design services that are not only discoverable but also provide interpretable information about their capabilities, the service discoverability principle provides guidelines that could be applied during the service-oriented analysis phase of the service delivery process.

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=== Specific to digital media ===
In relation to audiovisual content, according to the meaning given by the Canadian Radio-television and Telecommunications Commission (CRTC) for the purpose of its 2016 Discoverability Summit, discoverability can be summed up to the intrinsic ability of given content to "stand out of the lot", or to position itself so as to be easily found and discovered. A piece of audiovisual content can be a movie, a TV series, music, a book (eBook), an audio book or podcast. When audiovisual content such as a digital file for a TV show, movie, or song, is made available online, if the content is "tagged" with identifying information such as the names of the key artists (e.g., actors, directors and screenwriters for TV shows and movies; singers, musicians and record producers for songs) and the genres (for movies genres, music genres, etc.).
When users interact with online content, algorithms typically determine what types of content the user is interested in, and then a computer program suggests "more like this", which is other content that the user may be interested in. Different websites and systems have different algorithms, but one approach, used by Amazon (company) for its online store, is to indicate to a user: "customers who bought x also bought y" (affinity analysis, collaborative filtering). This example is oriented around online purchasing behaviour, but an algorithm could also be programmed to provide suggestions based on other factors (e.g., searching, viewing, etc.).
Discoverability is typically referred to in connection with search engines. A highly "discoverable" piece of content would appear at the top, or near the top of a user's search results. A related concept is the role of "recommendation engines", which give a user recommendations based on his/her previous online activity. Discoverability applies to computers and devices that can access the Internet, including various console video game systems and mobile devices such as tablets and smartphones. When producers make an effort to promote content (e.g., a TV show, film, song, or video game), they can use traditional marketing (billboards, TV ads, radio ads) and digital ads (pop-up ads, pre-roll ads, etc.), or a mix of traditional and digital marketing.
Even before the user's intervention by searching for a certain content or type of content, discoverability is the prime factor which contributes to whether a piece of audiovisual content will be likely to be found in the various digital modes of content consumption. As of 2017, modes of searching include looking on Netflix for movies, Spotify for music, Audible for audio books, etc., although the concept can also more generally be applied to content found on Twitter, Tumblr, Instagram, and other websites. It involves more than a content's mere presence on a given platform; it can involve associating this content with "keywords" (tags), search algorithms, positioning within different categories, metadata, etc. Thus, discoverability enables as much as it promotes. For audiovisual content broadcast or streamed on digital media using the Internet, discoverability includes the underlying concepts of information science and programming architecture, which are at the very foundation of the search for a specific product, information or content.
== Applications ==
=== Within a webpage ===
Within a specific webpage or software application ("app"), the discoverability of a feature, content or link depends on a range of factors, including the size, colour, highlighting features, and position within the page. When colour is used to communicate the importance of a feature or link, designers typically use other elements as well, such as shadows or bolding, for individuals, who cannot see certain colours. Just as traditional paper printing created other physical locations that stood out, such as being "above the fold" of a newspaper versus "below the fold", a web page or app's screenview may have certain locations that give features additional visibility to users, such as being right at the bottom of the web page or screen.
The positional advantages or disadvantages of various locations depend on different cultures and languages (e.g., left to right vs. right to left). Some locations have become established, such as having toolbars at the top of a screen or webpage. Some designers have argued that commonly used features (e.g., a print button) should be much more visually prominent than very rarely used features. Some features cannot be seen, but there is a convention that if the user places the mouse cursor in a certain area, then a toolbar or function option will become visible. In general, because of the smaller screen of mobile devices, controls are often not placed right in the centre of the screen, because that is where the user views content or text.
Some organizations try to increase the discoverability of a certain feature by adding animation, such as a moving "click here" icon. As of 2017, the addition of motion sensors and geotracking to mobile devices has made webpage design for discoverability more complex, because smartphones and tablets are typically capable of having many more inputs from the user than a 1980s era desktop, including "swiping" the touchscreen, touching images on the screen, or tilting the device. One of the challenges in webpage and app design is that the degree of sophistication and experience of users with navigating in the webpage or app environment varies a great deal, from individuals who are new to using these applications at one extreme to experienced computer users.

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=== Internet search ===
For items that are searched for online, the goal of discoverability is to be at or near the top of the search results. Organizations may make efforts to make it more likely, that "their" content or webpages are at the top, or close to the top, of search results; these approaches are often collectively called search engine optimization (SEO). Note that when an organization takes action to increase the SEO of its website, this does not normally involve changes to the search engine itself; rather, it involves adding metadata tags and original content, among other strategies, to increase the "visibility" of the website to search engine algorithms.
Recent discussions of discoverability have also considered AI-generated answer systems, in which visibility may depend not only on ranking in conventional search results but also on whether sources are selected, cited, and synthesized in generated responses.
==== Services ====
In a service delivery context, the application of this principle requires collecting information about the service during the service analysis phase as during this phase; maximum information is available about the service's functional context and the capabilities of the service. At this stage, the domain knowledge of the business experts could also be enlisted to document meta-data about the service. In the service-oriented design phase, the already gathered meta-data could be made part of the service contract. The OASIS SOA-RM standard specifies service description as an artifact that represents service meta-data.
To make the service meta-data accessible to interested parties, it must be centrally accessible. This could either be done by publishing the service-meta to a dedicated 'service registry' or by simply placing this information in a 'shared directory'. In case of a 'service registry', the repository can also be used to include QoS, SLA and the current state of a service.
=== Voice user interfaces ===
Voice user interfaces may have low discoverability if users are not aware of the commands that they are able to say, so these interfaces may display a list of available commands to help users find them.
== Metadata types ==
=== Functional ===
This is the basic type of meta-information that expresses the functional context of the service and the details about the product, content, or service's capabilities. The application of the standardized service contract principle helps to create the basic functional meta-data in a consistent manner. The same standardization should be applied when the same meta-information is being outside the technical contract of the service e.g. when publishing information to a service registry.
For general items, the data that might be used to categorize them may include:
Name of product, content or service (for audiovisual content, this would be song name, or TV show/movie title)
Name of manufacturer, designer, creators (for audiovisual content, this would be names of director/producer/artists)
Technical data (size, weight, height for physical items, or in the case of digital files, compression approach, file size)
For items which can identify their location via embedded sensors (such as with Internet of things geolocation data), location of use/access)
=== Quality of service ===
For services, to know about the service behavior and its limitations, and about the user experience, all of this information needs to be documented within the service registry. This way potential consumers can use this meta-information by comparing it against their performance requirements.
== Considerations ==
=== Services ===
The effective application of this design principle requires that the meta-information recorded against each service needs to be consistent and meaningful. This is only possible if organization-wide standards exist that enforce service developers to record the required meta-data in a consistent way. The information recorded as the meta-data for the service needs to be presented in a way so that both technical and non-technical IT experts can understand the purpose and the capabilities of the service, as an evaluation of the service may be required by the business people before the service is authorized to be used.
This principle is best applied during the service-oriented analysis phase as during this time, all the details about the service's purpose and functionality are available. Although most of the service design principles support each other in a positive manner, however, in case of service abstraction and service discoverability principle, there exists an inversely proportional relationship. This is because as more and more details about the service are hidden away from the service consumers, less discoverable information is available for discovering the service. This could be addressed by carefully recording the service meta-information so that the inner workings of the service are not documented within this meta-information.

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=== Algorithms ===
In the digital economy, sophisticated algorithms are required for the analysis of the ways that end users search for, access and use different content or products online. Thus, not only is metadata created regarding the content or product, but also data about specific users' interaction with this content. If a social media website has a user profile for a given person, indicating demographic information (age, gender, location of residence, employment status, education, etc.), then this website can collect and analyse information about tendencies and preferences of a given user or a subcategory of users. This raises potential privacy concerns.
Algorithms have been called “black boxes”, because the factors used by the leading websites in their algorithms are typically proprietary information which is not released to the public. While a number of search engine optimization (SEO) firms offer the services of attempting to increase the ranking of a client's web content or website, these SEO firms do not typically know the exact algorithms used by Google and Facebook. Web crawlers can only access 26% of new online content "...by recrawling a constant fraction of the entire web".
One concern raised with the increasing role of algorithms in search engines and databases is the creation of filter bubbles. To give a practical example, if a person searches for comedy movies online, a search engine algorithm may start mainly recommending comedies to this user, and not showing him or her the range of other films (e.g., drama, documentary, etc.). On the positive side, if this person only likes comedy films, then this restricted "filter" will reduce the information load of scanning through vast numbers of films. However, various cultural stakeholders have raised concerns about how these filter algorithms may restrict the diversity of material that is discoverable to users. Concerns about the dangers of "filter bubbles" have been raised in regards to online news services, which provide types of news, news sources, or topics to a user based on his/her previous online activities. Thus a person who has previously searched for Fox TV content will mainly be shown more Fox TV content and a person who has previously searched for PBS content will be shown more PBS search results, and so on. This could lead to news readers becoming only aware of a certain news source's viewpoints.
The search behaviour of video content viewers has changed a great deal with increasing popularity of video sharing websites and video streaming. Whereas a typical TV show consumer of the 1980s would read a print edition of TV Guide to find out what shows were on, or click from channel to channel ("channel surfing") to see if any shows appealed to them, in the 2010s, video content consumers are increasingly watching on screens (either smart TVs, tablet computer screens or smartphones), that have a computerized search function and often automated algorithm-created suggestions for the viewer. With this search function, a user can enter the name of a TV show, producer, actor, screenwriter or genre to help them find content of interest to them. If the user is using a search engine on a smart device, this device may transmit information about the user's preferences and previous online searches to the website. Furthermore, in the 1980s, the type or brand of television a user was watching on did not affect his/her viewing habits. However, a person searching for TV shows in the 2010s on different brands of computerized smart TVs will probably get different search results for the same search term.
=== Limitations ===
For organizations that are trying to get maximal user uptake of their product, discoverability has become an important goal. However, achieving discovery does not automatically translate into market success. For example, if the hypothetical online game "xyz" is easily discoverable, but it will not function on most mobile devices, then this video game will not perform well in the mobile game market, despite it being at the top of search results. As well, even if the product functions, that is it runs or plays properly, as well, users may not like the product.
In the case that a user does like a certain online product or service, the discoverability has to be repeatable. If the user cannot find the product or service on a subsequent search, she or he may no longer look for this product/service, and instead shift to a substitute that is easily and reliably findable. It is not enough to make the online product or service discoverable for only a short period, unless the goal is only to create “viral content" as part of a short-term marketing campaign.
== See also ==
Findability
Information foraging
Service-oriented architecture
WSDL
== References ==

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Discrete debris accumulation (DDA) is a non-genetic term in mountain glacial geology to aid identification of non-lithified sediments on a valley or mountain slope or floor. It is intended that the debris accumulation is discrete such that it can be mapped, in the field and/or from aerial or satellite imagery. The origin or formative process may well not be known clearly or be changed by subsequent investigators it is advisable to have a non-genetic field reference so that discussion can then be used to ascertain, if possible, the origin. Mountain areas may currently have glaciers (glacierized) or have had glaciers (glaciated) or be subject to forms of periglacial activity. A moraine would be an easily identified DDA as would an esker. Although scree (talus) is generally easily identified and mapped, these deposits may be modified by ice, avalanches or downslope movement to create essentially new landforms. Many small slope failures and landslides can give the appearance of moraines or protalus ramparts on slopes. After mapping as a DDA, further investigation might draw light on the origin of the feature.
The term was apparently first used by Sven Lukas for a very specific feature in Svalbard.
Independently, it was suggested in the literature in W. B. Whalley and subsequently in Whalley, 2012 as relating to the basic definition and usage as above. This book chapter provides several photographic examples.
The 'cirque infills' described by Hätterstrand et al. (2008) in the Khibiny Mountains, Kola Peninsula could be described as discrete debris accumulations, although their origin is postulated by these authors as being moraine remnants of an ice sheet pushing into these cirques rather than as rock glaciers formed within the cirques.
A recent term introduced by Brighenti et al. is 'Cold Rocky Landforms' (CRLs) as a more general term including landforms generally identified as: protalus ramparts, valley-wall rock glaciers, talus (or scree) slopes and 'ice-embedded' moraines. 'Structurally, CRLs have a surface mantle of rocky debris and interiors composed of ice and rock'. However, it is by no means clear that any CRL necessarily contains ice in any form. Ice would not be present in areas that have long since lost any ice, whether from glaciers or snowbanks such as in upland Britain, where DDAs, as difficult to map entities, are known to exist.
== References ==

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Downstate may refer to:
Downstate Illinois, the portion of the U.S. state of Illinois south of the Chicago metropolitan area
Downstate (play), a 2018 tragicomedy about sex offenders set in Downstate Illinois
Downstate New York, the southeastern portion of the U.S. state of New York, including New York City
SUNY Downstate Medical Center, sometimes referred to as "Downstate"
== See also ==
Upstate (disambiguation)
Down south (disambiguation)

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In geography, a dry point is an area of firm or flood-free ground in an area of wetland, marsh or flood plains. The term typically applies to settlements, and dry point settlements were common in history.
In the United Kingdom extreme examples of dry point settlements include Ely, situated on a small hill in the marshy Fens; Glastonbury, situated on a low hill in the marshy Somerset Levels; and Wareham surrounded by flood plains beside Poole Harbour.
A dry point has the advantages of flood protection, fertile soil (due to previous floodings which would have deposited silt on the land) and fairly flat land which is ideal for agriculture and building.
== References ==
== External links ==
Media related to Dry point at Wikimedia Commons

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An endorheic lake (also called a sink lake or terminal lake) is a collection of water within an endorheic basin, or sink, with no evident outlet. Endorheic lakes are generally saline as a result of being unable to get rid of solutes left in the lake by evaporation. These lakes can be used as indicators of anthropogenic change, such as irrigation or climate change, in the areas surrounding them. Lakes with subsurface drainage are called cryptorheic.
== Components of endorheic lakes ==
The two main ways that endorheic lakes accumulate water are through river flow into the lake (discharge) and precipitation falling into the lake. The collected water of the lake, instead of discharging, can only be lost due to either evapotranspiration or percolation (water sinking underground, e.g., to become groundwater in an aquifer). Because of this lack of an outlet, endorheic lakes are mostly salt water rather than fresh water. The salinity in the lake gradually builds up through years as water evaporates and leaves its solutes behind.
== Similar types of lakes ==
Depending on water losses, precipitation, and inflow (e.g., a spring, a tributary, or flooding), the temporal result of a lake in a sink may change. The lake could be a persistent lake, an intermittent lake, a playa lake (temporarily covered with water), or an ephemeral lake, which completely disappears (e. g. by evaporation) before reappearing in wetter seasons. These terms (playa, ephemeral lake, etc.) are sometimes used interchangeably, but there has been activity tending towards defining meanings for each term.
== Anthropogenic effects ==
Many endorheic lakes exist in arid or semi-arid climates. Because these climates have limited rainfall, but also a high possibility of evaporation, endorheic lakes in these regions often experience flux in their water levels. This flux can be aggravated by anthropogenic intrusions (e.g. global warming).
In Central Asia, a large percentage of water for farming comes from surface water, like endorheic lakes, rather than precipitation. Because of the overall lack of precipitation, farming in this area can only be sustained by irrigation. Massive amounts of irrigation in agrarian Central Asia have led to the reduction in size of endorheic lakes. The Aral Sea was once the second largest endorheic lake in the world, but anthropogenic effects such as bad irrigation practices have led to this lake's drastic decrease in size and transition into a desert, the Aralkum Desert.
Endorheic lakes, because of the closed nature of their systems, are sensitive to new conditions. Records of previous environmental change are preserved in lake sediments in endorheic lakes that are being affected by climate change; these natural records can give information about past climates and conditions of the lake. Research on these lake sediments could lead to these lakes becoming archives of the effects of climate change. There is early evidence that in regions affected by irrigation the majority of endorheic lake area may have already been lost.
== List of endorheic lakes ==
=== Africa ===
Afar Depression (Great Rift Valley in East Africa)
Lake Chad (Central Africa)
Lake Rukwa (East Africa)
Lake Turkana (East Africa)
=== Asia ===
Aral Sea (Kazakhstan; Uzbekistan)
Lake Balkhash (Kazakhstan)
Caspian Sea (Iran; Azerbaijan; Russia; Kazakhstan; Turkmenistan)
Dead Sea (Israel; Jordan; West Bank)
Gavkhouni (Isfahan, Iran)
Hamun-e Jaz Murian (Kerman and Sistan and Baluchistan, Iran)
Hamun Lake (Iran)
Issyk-Kul (Kyrgyzstan)
Lake Urmia (West Azerbaijan province, Iran)
Lake Van (Turkey)
Maharloo Lake (Fars province, Iran)
Namak Lake (Qom, Iran)
Qarhan Playa (Qinghai, China)
Shalkar (Kazakhstan)
Pangong Tso (Ladakh, India; Tibet, China)
=== Australia ===
Kumpupintil Lake (Western Australia)
Lake Eyre (South Australia)
Lake George (New South Wales)
=== Europe ===
Botkul (Kazakhstan–Russia border)
Caspian Sea
Lake Neusiedl (Austria, Hungary)
Lake Prespa (Balkans)
Lake Trasimeno (Italy)
=== North America ===
Carson Sink (Churchill County, Nevada, U.S.)
Devils Lake (North Dakota, U.S.)
Devil's Lake (Wisconsin, U.S.)
Lake Enriquillo (Dominican Republic)
Etang Saumâtre (Haiti)
Great Salt Lake (Utah, U.S.)
Humboldt Sink (northwestern Nevada, U.S.)
Mono Lake (Mono County, California, U.S.)
Owens Lake (Eastern Sierra, California, U.S.)
Pyramid Lake (western Nevada, U.S.)
Quinn River Sink (northwestern Nevada, U.S.)
Salton Sink (southern California, U.S.)
Eagle Lake (British Columbia, Canada)
Choelquoit Lake (British Columbia, Canada)
Martin Lake (British Columbia, Canada)
Manitou Lake (Saskatchewan, Canada)
Lake Xochimilco (Mexico City, Mexico)
=== South America ===
Lake Poopó (Altiplano part of Bolivia)
== See also ==
Sinkhole – Geologically-formed topological depression
== References ==

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In stratigraphy and geology, an eonothem is the totality of rock strata laid down in the stratigraphic record deposited during a certain eon of the continuous geologic timescale. The eonothem is not to be confused with the eon itself, which is a corresponding division of geologic time spanning a specific number of (hundreds of millions of) years, during which rocks were formed that are classified within the eonothem. Eonothems have the same names as their corresponding eons, which means during the history of the Earth only four eonothems were formed. Oldest to newest these are the Hadean, Archean, Proterozoic, and Phanerozoic. A rock stratum, fossil or feature present in the "upper Phanerozoic" eonothem would therefore have originated within the "later Phanerozoic" eon. In practice, the rock column is discontinuous:
Technically, a complete geologic record doesn't occur anywhere. For such a record to develop would require the area to have been receiving sedimentary deposits continually ever since the origin of the earth. Nowhere is such a situation known to exist. If it did exist, we could not effectively look at the strata because they would still be buried, and modern strata would continue to be deposited on top of them.
The earth's surface has been far too dynamic to allow that to occur anywhere. No area has been in such a static condition throughout the earth's long history. Areas that have had sediment deposited on them at one time are later uplifted and eroded. In some places this has occurred many times. There is ample evidence to prove such a sequence of events.
Eonothems, despite discontinuities (locally missing strata or unconformities), can be compared to others where the rock record is more complete and, by correlation of points of correspondence, be fixed appropriately within the eon. They are therefore useful as broad chronostratigraphic units, specifying approximate age within the timelines within the rock column.
Eonothems are subdivided into erathems and their smaller subdivisions within geology and paleobiology and their sub-fields, and a whole system of cross-disciplinary classification by strata is in place with oversight by the International Commission on Stratigraphy.
Eonothems are not often used in practice as expert dating estimates can be and usually are specified into the more refined timelines of smaller chronostratigraphic units, which can be subdivided in turn down to the many defined stages, the smallest formally recognised units used in dating. (see the hierarchy of comparative units, five each for time division types and five for the rock record types.)
== Dating standards ==
Global Standard Stratigraphic Ages (GSSAs) are defined by the International Commission on Stratigraphy and are used primarily for time-dating rock layers older than 630 million years ago (mya), before a good fossil record exists.
For more recent periods, a Global Boundary Stratotype Section and Point (GSSP), largely based on research progress in geobiology and improved methods of fossil dating is used to define such boundaries. In contrast to GSSAs, GSSPs are based on important events and transitions within a particular stratigraphic section. In older sections, there is insufficient fossil record or well preserved sections to identify the key events necessary for a GSSP so GSSAs are defined based on fixed dates.
== Etymology ==
Eonothem derives from eon 'age', a Latin transliteration from the koine Greek word αἰών (aion) from the archaic αἰϝών (aiwon), and thema 'that which is placed or laid down; subject of a discourse'.
== See also ==
=== Multidiscipline comparison ===
Chronostratigraphy
Lithostratigraphy
Geologic record
=== Related other topics ===
Body form
Fauna (animals)
Type locality
== Notes ==
== References ==
Hedberg, H.D., (editor), International stratigraphic guide: A guide to stratigraphic classification, terminology, and procedure, New York, John Wiley and Sons, 1976
International Stratigraphic Chart from the International Commission on Stratigraphy
USA National Park Service
Washington State University Archived 2011-07-26 at the Wayback Machine
Web Geological Time Machine
Eon or Aeon, Math Words - An alphabetical index
== External links ==
The Global Boundary Stratotype Section and Point (GSSP): overview
Chart of The Global Boundary Stratotype Sections and Points (GSSP): chart
Geotime chart displaying geologic time periods compared to the fossil record.

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In stratigraphy, paleontology, geology, and geobiology, an erathem is the total stratigraphic unit deposited during a certain corresponding span of time during an era in the geologic timescale.
It can therefore be used as a chronostratigraphic unit of time which delineates a large span of years – less than a geological eon, but greater than its successively smaller and more refined subdivisions (geologic periods, epochs, and geologic ages). By 3,500 million years ago (Mya) simple life had developed on earth (the oldest known microbial fossils in Australia are dated to this figure). The atmosphere was a mix of noxious and poisonous gases (methane, ammonia, sulfur compounds, etc. – a so-called reducing atmosphere lacking much free oxygen which was bound up in compounds).
These simple organisms, cyanobacteria ruled the still cooling earth for approximately a billion years and gradually transformed the atmosphere to one containing free oxygen. These changes, along with tectonic activity left chemical trails (red bed formation, etc.) and other physical clues (magnetic orientation, layer formation factors) in the rock record, and it is these changes along with the later richer fossil record which specialists use to demarcate times early in planet earth's history in various disciplines.
Erathems are not often used in practice. While they are subdivisions of eonothems and are themselves subdivided into systems, dating experts prefer the finer resolution of smaller spans of time when evaluating strata.
Erathems have the same names as their corresponding eras. The Phanerozoic eonothem can thus be divided into Cenozoic, Mesozoic, and Paleozoic erathems. Similarly, the Proterozoic eonothem is divided youngest to oldest into the Neoproterozoic, Mesoproterozoic and Paleoproterozoic erathems, and the Archean eon and eonothem are divided similarly into the Neoarchean, Mesoarchean, Paleoarchean and the Eoarchean, for which a lower (oldest) limit is undefined.
== See also ==
=== Multidiscipline comparison ===
=== Related other topics ===
Body form
European Mammal Neogene
Geologic time scale
New Zealand geologic time scale
North American Land Mammal Age
Fauna (animals)
Type locality
List of GSSPs
== Notes ==
== References ==
Gehling, James; Jensen, Sören; Droser, Mary; Myrow, Paul; Narbonne, Guy (March 2001). "Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland". Geological Magazine. 138 (2): 213–218. Bibcode:2001GeoM..138..213G. doi:10.1017/S001675680100509X. hdl:10662/24314. S2CID 131211543. 1.
Hedberg, H.D., (editor), International stratigraphic guide: A guide to stratigraphic classification, terminology, and procedure, New York, John Wiley and Sons, 1976
International Stratigraphic Chart from the International Commission on Stratigraphy
US National Park Service description of geographic time
Washington State University description of geographic time Archived 2011-07-26 at the Wayback Machine
Web Geological Time Machine
Eon or Aeon, Math Words – An alphabetical index
== External links ==
The Global Boundary Stratotype Section and Point (GSSP): overview
Chart of The Global Boundary Stratotype Sections and Points (GSSP): chart
Geotime chart displaying geologic time periods compared to the fossil record – Deals with chronology and classifications for laymen (not GSSPs)

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In the context of spatial analysis, geographic information systems, and geographic information science, a field is a property that fills space, and varies over space, such as temperature or density. This use of the term has been adopted from physics and mathematics, due to their similarity to physical fields (vector or scalar) such as the electromagnetic field or gravitational field. Synonymous terms include spatially dependent variable (geostatistics), statistical surface ( thematic mapping), and intensive property (physics and chemistry) and crossbreeding between these disciplines is common. The simplest formal model for a field is the function, which yields a single value given a point in space (i.e., t = f(x, y, z) )
== History ==
The modeling and analysis of fields in geographic applications was developed in five essentially separate movements, all of which arose during the 1950s and 1960s:
Cartographic techniques for visualizing fields in thematic maps, including choropleth and isarithmic maps. In theoretical cartography, the concept of a "statistical surface" had gained wide acceptance by 1960, using the metaphor of a third dimension to conceptualize continuous quantitative variation in a variable. The statistical surface as a concept and term has persisted in cartography to the present.
The quantitative revolution of geography, starting in the 1950s, and leading to the modern discipline of spatial analysis; especially techniques such as the Gravity model and models of potential. Although they did not specifically use the term field, they were incorporating the mathematics of fields from physics.
The development of raster GIS models and software, starting with the Canadian Geographic Information System in the 1960s, which mapped fields such as land cover type.
The technique of cartographic modeling, pioneered by Ian McHarg in the 1960s and later formalized for digital implementation in raster GIS by Dana Tomlin as map algebra.
Geostatistics, which arose from mining geology starting in the 1950s, was originally developed around methods for interpolating the continuous variation in fields from finite point samples. Terms such as regionalized variable were often used in the literature rather than "field."
While all of these incorporated similar concepts, none of them used the term "field" consistently, and the integration of the underlying conceptual models of these applications has only occurred since 1990 as part of the emergence of Geographic information science.
During the 1980s, the maturation of the core technologies of GIS enabled academics to begin to theorize about the fundamental concepts of geographic space upon which the software seemed to be based. Donna Peuquet, Helen Couclelis, and others began to recognize that the competing vector and raster data models were based on a duality between a view of the world as filled with objects and a "location-based" or "image-based" view of the world filled with properties of location. Michael F. Goodchild introduced the term field from physics by 1992 to formalize the location-property conceptual model. During the 1990s, the raster-vector debate transformed into a debate over whether the "object view" or the "field view" was dominant, whether one reflected the nature of the real world and the other was merely a conceptual abstraction.
== The nature and types of fields ==
Fields are useful in geographic thought and analysis because when properties vary over space, they tend to do so in spatial patterns due to underlying spatial structures and processes. A common pattern is, according to Tobler's first law of geography: "Everything is related to everything else, but near things are more related than distant things." That is, fields (especially those found in nature) tend to vary gradually, with nearby locations having similar values. This concept has been formalized as spatial dependence or spatial autocorrelation, which underlies the method of geostatistics. A parallel concept that has received less publicity, but has underlain geographic theory since at least Alexander von Humboldt is spatial association, which describes how phenomena are similarly distributed. This concept is regularly used in the method of map algebra.
Even though the basic concept of a field came from physics, geographers have developed independent theories, data models, and analytical methods. One reason for this apparent disconnect is that although geographic fields may show patterns similar to gravity and magnetism, they can have a very different underlying nature, and be created by very different processes. Geographic fields can be classified by their ontology or fundamental nature as:
Natural fields, properties of matter that are formed at scales below that of human perception, and thus appear continuous at human scales, such as temperature or soil moisture.
Aggregate fields, statistically constructed properties of aggregate groups of individuals, such as Population density or tree canopy coverage.
Fields of potential or influence, which measure conceptual, non-material quantities (and are thus most closely related to the fields of physics), such as the probability that a person at any given location will prefer to use a particular grocery store.
Geographic fields can also be categorized according to the type of domain of the measured variable, which determines the pattern of spatial change. A continuous field has a continuous (real number) domain, and typically shows gradual change over space, such as temperature or soil moisture; a discrete field, also known as a categorical coverage or area-class map, has a discrete (often qualitative) domain, such as land cover type, soil class, or surface geologic formation, and typically has a pattern of regions of homogeneous value with boundaries (or transition zones) where the value changes.
Both scalar (having a single value for any location) and vector (having multiple values for any location representing different but related properties) fields are found in geographic applications, although the former is more common.
Geographic fields can exist over a temporal domain as well as space. For example, temperature varies over time as well as location in space. In fact, many of the methods used in time geography and similar spatiotemporal models treat the location of an individual as a function or field over time.

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== Representation models ==
Because, in theory, a field consists of an infinite number of values at an infinite number of locations, exhibiting a non-parametric pattern, only finite sample-based representations can be used in analytical and visualization tools such as GIS, statistics, and maps. Thus, several conceptual, mathematical and data models have emerged to approximate fields, including:
An irregular point sample, a finite set of sample locations, at either random or strategic locations. Examples include data from weather stations or Lidar point clouds.
A lattice, or regular point sample, consisting of locations that are evenly spaced in each cartesian direction. These are typically stored in a Raster data structure. Examples include the Digital elevation model.
A Choropleth, an irregular a priori partition, in which space is partitioned into regions unrelated to the field itself, such as countries, and field values are summarized over each region. These are typically stored using vector polygons. Examples would include Population density by county, derived from census returns.
A Chorochromatic map or Area-class map, an irregular strategic partition usually used for discrete fields, in which space is partitioned into regions intended to match regions of homogeneous field value, typically stored as vector polygons. Examples include maps of geologic layers or vegetation stands.
A grid or regular partition, in which space is partitioned into equal regions (often squares), and field values are summarized over each region. These are also typically stored in a Raster data structure. Examples include the electromagnetic reflectance signature of land cover as represented in Remote sensing imagery.
A surface, in which the field is conceptualized as a third spatial dimension, and three dimensional data models are used for representation. Examples include the Triangulated irregular network (TIN).
An isarithm or isopleth, in which lines are drawn connecting locations of equal field value, partitioning space into regions of similar value. An example is the Contour line of elevation, commonly found on topographic maps.
The choice of representation model typically depends on a variety of factors, including the analyst's conceptual model of the phenomenon, the devices or methods available to measure the field, the tools and techniques available to analyze or visualize the field, and the models being used for other phenomena with which the field in question will be integrated. It is common to transform data from one model to another; for example, an isarithmic weather map of temperature is often generated from a raster grid, which was created from raw weather station data (an irregular point sample). Every such transformation requires Interpolation to estimate field values between or within the sample locations, which can lead to a number of forms of uncertainty, or misinterpretation traps such as the Ecological fallacy and the Modifiable areal unit problem. This also means that when data is transformed from one model to another, the result will always be less certain than the source.
== See also ==
Feature (geography)
Region (geography)
== References ==

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In materials science, friability ( FRY-ə-BIL-ə-tee), the condition of being friable, describes the tendency of a solid substance to break into smaller pieces under stress or contact, especially by rubbing. The opposite of friable is indurate.
Substances that are designated hazardous, such as asbestos or crystalline silica, are often said to be friable if small particles are easily dislodged and become airborne, and hence respirable (able to enter human lungs), thereby posing a health hazard.
Tougher substances, such as concrete, may also be mechanically ground down and reduced to finely divided mineral dust. However, such substances are not generally considered friable because of the degree of difficulty involved in breaking the substance's chemical bonds through mechanical means. Some substances, such as polyurethane foams, show an increase in friability with exposure to ultraviolet radiation, as in sunlight.
Friable is sometimes used metaphorically to describe "brittle" personalities who can be "rubbed" by seemingly-minor stimuli to produce extreme emotional responses.
== General ==
A friable substance is any substance that can be reduced to fibers or finer particles by the action of a small amount of pressure or friction, such as rubbing or inadvertently brushing up against the substance. The term could also apply to any material that exhibits these properties, such as:
Ionically bound substances that are less than 1 kg/L in density
Clay tablets
Crackers
Mineral fibers
Polyurethane (foam)
Aerogel
== Geological ==
Friable and indurated are terms used commonly in soft-rock geology, especially with sandstones, mudstones, and shales to describe how well the component rock fragments are held together.
Examples:
Clumps of dried clay
Chalk
Perlite
== Medical ==
The term friable is also used to describe tumors in medicine. This is an important determination because tumors that are easily torn apart have a higher risk of malignancy and metastasis.
Examples:
Some forms of cancer, such as atrial myxoma
An inflamed gallbladder
== Pharmaceutical ==
Friability testing is a laboratory technique used by the pharmaceutical industry to test the durability of tablets during transit. This testing involves repeatedly dropping a sample of tablets over a fixed time, using a rotating wheel with a baffle. The result is inspected for broken tablets, and the percentage of tablet mass lost through chipping. A typical specification will allow a non-zero percentage of chipping, and zero broken tablets.
== See also ==
Asbestos abatement
Frangibility
Spall
== References ==
== External links ==
UK Advisory Committee Treatise On Friable Ceramic Fibres Archived 2017-07-06 at the Wayback Machine

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This is a list of common atlas and gazetteer abbreviations. These abbreviations are not always used consistently between publications; some terms have fallen out of use over time. Older gazetteers and atlases often neglect to define abbreviations and underlying terms. Gazetteer and map abbreviations can show up in several forms: upper or lower case, with or without periods, sometimes with hyphens (e.g., Post Village may be P.V., PV, p.v., or p-v).
This list does not include direction headings (e.g., N. or No. for north, etc.), which are generally clear.
== References ==
== See also ==
Administrative division

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In classical Roman religion, a genius loci (pl.: genii locorum) was the protective spirit of a place. It was often depicted in religious iconography as a figure holding attributes such as a cornucopia, patera (libation bowl), or snake. Many Roman altars found throughout the Western Roman Empire were dedicated to a particular genius loci. The Roman imperial cults of the Emperor and the imperial house developed in part in connection with the sacrifices made by neighborhood associations (vici) to the local genius. These 265 local districts had their cult organised around the Lares Compitales (guardian spirits or lares of the crossroads), which the emperor Augustus transformed into Lares Augusti along with the Genius Augusti. The emperor's genius is then regarded as the genius loci of the Roman Empire as a whole.
Roman examples of these genii can be found, for instance, at the church of St. Giles, Tockenham, Wiltshire, England, where the genius loci is depicted as a relief in the wall of a Norman church built of Roman material. This shows "a youthful and curly-haired Roman Genius worked in high relief, holding a cornucopia in his left hand and a patera in his right", which previously has been "erroneously identified as Asclepius".
== Asian usage ==
The numinous spirits of places in Asia are still honored today in city pillar shrines, outdoor spirit houses and indoor household and business shrines.
== Western usage ==
In contemporary usage, genius loci usually refers to a location's distinctive atmosphere or a "spirit of the place" rather than necessarily a guardian spirit. An example of contemporary usage might be "Light reveals the genius loci of a place."
== Art and architecture ==
Alexander Pope made the genius loci an important principle in garden and landscape design with the following lines from Epistle IV, to Richard Boyle, Earl of Burlington:
Pope's verse laid the foundation for one of the most widely agreed principles of landscape architecture, that landscape designs should always be adapted to the context in which they are located.
A priori, archetype, and genius loci are the primary principals of Neo-Rationalism or New Rationalism. Pioneered by the Italian architect Aldo Rossi, Neo-Rationalism developed in the light of a re-evaluation of the work of Giuseppe Terragni and gained momentum through the work of Giorgio Grassi. Characterized by elemental vernacular forms and an adaptation to the existing environment, the Neo-Rationalist style has adherents beyond architecture in the greater world of art.
In the context of modern architectural theory, genius loci has profound implications for place-making, falling within the philosophical branch of phenomenology. This field of architectural discourse is explored most notably by the theorist Christian Norberg-Schulz in his book, Genius Loci: Towards a Phenomenology of Architecture.
== Modern fantasy ==
Adaptations of the original concept of the genius loci appear in some modern fantasy works.
Tom Bombadil in The Lord of the Rings has been described by Tolkien scholar Tom Shippey as the genius loci of the Old Forest, a wooded land bordering the Shire.
In the Dungeons and Dragons 3.0 edition book the Epic Level Handbook, the genius loci is a malign, powerful ooze that mimics the landscape and has no intelligence of its own. It can magically enslave a visitor whose mind affects the genius loci's behaviour. It is spontaneously generated when a place is undisturbed for a long time.
In The Dresden Files, a genius loci is an elemental spirit of a place. The island of Demonreach has a genius loci, also named Demonreach, which is omniscient regarding the island. Wizards can form a spiritual connection with a genius loci and the place it represents.
The Rivers of London series of novels by Ben Aaronovitch feature many beings described as genii locorum, primarily those of the River Thames and its tributaries.
== See also ==
Jinn
Kami
Landvættir
Wight
Seonangshin, Korean equivalent
Spirit house
Pukwudgie
Rå
Hulder
Tomte
Tuatha Dé Danann
Leshy
Huldufólk
Nymph
Haltija
Chinese versions
Cheng Huang Gong (City God), Chinese official urban equivalent
Tu Di Gong (Earth Deity), Chinese locality equivalent
Dizhu shen (Landlord deity), Chinese equivalent for small regions like buildings
Jinushigami
Tutelary deity
Zashiki-warashi
Zeitgeist
== References ==
== Further reading ==
Patterson, Barry (2005). The Art of Conversation with the Genius Loci. Cappall Bann Books. ISBN 1-86163-169-3.
== External links ==
Essay on the Genius loci in landscape and garden design
Photographs of St. Giles, Tockenham, Wiltshire

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Genreflecting is the process of examining and analyzing the patterns and characteristics of literary genres—both fiction and recreational nonfiction—and using that analysis to identify titles with similar appeals to readers (i.e., read-alikes), in order to make reading suggestions to individuals who are looking for something to read.
The term "genreflecting" was first coined by Betty Rosenberg, a prominent library science educator, in 1982.
Since that time, the term has been adopted by readers' advisory in libraries and extended to nonfiction genres as well as fiction. A similar practice in retail bookstores is called "hand-selling."
== History ==
At the time the first edition of Rosenberg's Genreflecting was written, adding popular reading materials to library collections and recommending those titles to readers were controversial practices. Dr. Rosenberg's First Law of Reading—"Never apologize for your reading taste"—has since been adopted by growing numbers of librarians, and the field of readers' advisory has become increasingly central to the practice of librarianship.
Nancy Pearl, the well known model of the librarian action figure and author of Book Lust and More Book Lust, has promoted and further popularized the practice of readers' advisory within the library community and beyond.
In recent years, a number of online databases have been developed to assist readers' advisors find "read-alikes," including What Do I Read Next? (Gale Thomson), NoveList (EBSCO), The Reader's Advisor Online (Greenwood Publishing Group), Fiction Connection (Bowker), and Booklist Online (American Library Association).
== References ==
== Further reading ==
Rosenberg, Betty. (1982). Genreflecting: A Guide to Reading Interests in Genre Fiction. Littleton, CO: Libraries Unlimited. ISBN 978-0872873339
Herald, Diana Tixier. (2005). Genreflecting: A Guide to Popular Reading Interests (6th ed.). Westport, CT: Libraries Unlimited. ISBN 978-1591582861
Cords, Sarah Statz. (2006). The Real Story: A Guide to Nonfiction Reading Interests. Westport, CT: Libraries Unlimited. ISBN 978-1591582830
Saricks, Joyce G. (2009). The Readers' Advisory Guide to Genre Fiction (2nd ed.). Chicago, IL: ALA Editions. ISBN 978-0838909898

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In geographic information systems, a geocell (or geo-cell) is a patch on the surface of the Earth that is 1 degree of latitude by 1 degree of longitude in extent.
At the equator, a geocell is approximately a 111x111 kilometres (69 mi) square - but the east-west dimension of geocells gradually decreases and the shape of the geocell becomes increasingly trapezoidal towards the poles. At the North and South poles, geocells are distorted into long, thin triangles which are still approximately 111 kilometres (69 mi) in the north/south direction but with a base of just 969 metres (3,179 ft).
== References ==

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In geography, different geographic (scale) levels are distinguished:
The local scale level relates to a small area, usually a city or municipality;
The regional scale level relates to a larger area, usually a region, state or province;
The national scale level relates to a country;
The continental scale level refers to a continent;
The global scale applies to the entire world;
The fluvial scale level relates to river basins (this scale level is mainly used in the context of pollution, for example).
Within geography the use of geographic levels is also known as scales of analysis.
An area of several countries (such as the Middle East or West Africa) is sometimes counted under the continental scale level, sometimes under the regional scale. Actually, both are incorrect, because it does not include a continent but is larger than a country, while the regional scale is smaller than the national scale. Sometimes the international scale level is also used for this, but this term is not in general use.
== Use ==
The concept is used to describe, for example, disasters, climate models, cartographic matters, epidemiological studies or effects of human actions on the environment. Using the concept of Geographic levels it is easier to describe the scale, size and impact of a phonomenon.
Changing geographic levels helps to identify how people affected by their environment at different levels, from local to global.
This concept enables geographers to see hidden patterns and connections in the world.
Changing scale can uncover causes and effects of phenomena, offering a wider or more detailed view.
Geographers use scales to choose the right area for study, compare places, link human activity to environmental health, and avoid oversimplifying complex issues.
It is also used to present data.
== See also ==
Level of analysis
== References ==
== External links ==
https://wikitravel.org/en/Wikitravel:Geographical_hierarchy

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Geographic targeting is a viable way for resource allocation, especially to alleviate poverty in a country. In this context, public expenditure and policy interventions can be deployed to reach the neediest people in the poorest areas.
Geographical targeting for poverty alleviation employs a variety of techniques, such as database, and geographic information systems to construct poverty maps.
== References ==

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A geographical cluster is a localized anomaly, usually an excess of something given the distribution or variation of something else. Often it is considered as an incidence rate that is unusual in that there is more of some variable than might be expected. Examples would include: a local excess disease rate, a crime hot spot, areas of high unemployment, accident blackspots, unusually high positive residuals from a model, high concentrations of flora or fauna, physical features or events like earthquake epicenters etc...
Identifying these extreme regions may be useful in that there could be implicit geographical associations with other variables that can be identified and would be of interest. Pattern detection via the identification of such geographical clusters is a very simple and generic form of geographical analysis that has many applications in many different contexts. The emphasis is on localized clustering or patterning because this may well contain the most useful information.
A geographical cluster is different from a high concentration as it is generally second order, involving the factoring in of the distribution of something else.
== Geographical cluster detection ==
Identifying geographical clusters can be an important stage in a geographical analysis. Mapping the locations of unusual concentrations may help identify causes of these. Some techniques include the Geographical Analysis Machine and Besag and Newell's cluster detection method.
== References ==

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In geography and particularly in geographic information science, a geographic feature or simply feature (also called an object or entity) is a representation of phenomenon that exists at a location in the space and scale of relevance to geography; that is, at or near the surface of Earth. It is an item of geographic information, and may be represented in maps, geographic information systems, remote sensing imagery, statistics, and other forms of geographic discourse. Such representations of phenomena consist of descriptions of their inherent nature, their spatial form and location, and their characteristics or properties.
== Terminology ==
The term "feature" is broad and inclusive, and includes both natural and human-constructed objects. The term covers things which exist physically (e.g. a building) as well as those that are conceptual or social creations (e.g. a neighbourhood). Formally, the term is generally restricted to things which endure over a period. A feature is also discrete, meaning that it has a clear identity and location distinct from other objects, and is defined as a whole, defined more or less precisely by the boundary of its geographical extent. This differentiates features from geographic processes and events, which are perdurants that only exist in time; and from geographic masses and fields, which are continuous in that they are not conceptualized as a distinct whole.
In geographic information science, the terms feature, object, and entity are generally used as roughly synonymous. In the 1992 Spatial Data Transfer Standard (SDTS), one of the first public standard models of geographic information, an attempt was made to formally distinguish them: an entity as the real-world phenomenon, an object as a representation thereof (e.g. on paper or digital), and a feature as the combination of both entity and representation objects. Although this distinction is often cited in textbooks, it has not gained lasting nor widespread usage. In the ISO 19101 Geographic Information Reference Model and Open Geospatial Consortium (OGC) Simple Features Specification, international standards that form the basis for most modern geospatial technologies, a feature is defined as "an abstraction of a real-world phenomenon", essentially the object in SDTS.
== Types of features ==
=== Natural features ===
A natural feature is an object on the planet that was not created by humans, but is a part of the natural world.
==== Ecosystems ====
There are two different terms to describe habitats: ecosystem and biome. An ecosystem is a community of organisms. In contrast, biomes occupy large areas of the globe and often encompass many different kinds of geographical features, including mountain ranges.
Biotic diversity within an ecosystem is the variability among living organisms from all sources, including inter alia, terrestrial, marine and other aquatic ecosystems. Living organisms are continually engaged in a set of relationships with every other element constituting the environment in which they exist, and ecosystem describes any situation where there is relationship between organisms and their environment.
Biomes represent large areas of ecologically similar communities of plants, animals, and soil organisms. Biomes are defined based on factors such as plant structures (such as trees, shrubs, and grasses), leaf types (such as broadleaf and needleleaf), plant spacing (forest, woodland, savanna), and climate. Unlike biogeographic realms, biomes are not defined by genetic, taxonomic, or historical similarities. Biomes are often identified with particular patterns of ecological succession and climax vegetation.
==== Water bodies ====
A body of water is any significant and reasonably long-lasting accumulation of water, usually covering the land. The term "body of water" most often refers to oceans, seas, and lakes, but it may also include smaller pools of water such as ponds, creeks or wetlands. Rivers, streams, canals, and other geographical features where water moves from one place to another are not always considered bodies of water, but they are included as geographical formations featuring water.
Some of these are easily recognizable as distinct real-world entities (e.g. an isolated lake), while others are at least partially based on human conceptualizations. Examples of the latter are a branching stream network in which one of the branches has been arbitrarily designated as the continuation of the primary named stream; or a gulf or bay of a body of water (e.g. a lake or an ocean), which has no meaningful dividing line separating it from the rest of the lake or ocean.
==== Landforms ====
A landform comprises a geomorphological unit and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such is typically an element of topography. Landforms are categorized by features such as elevation, slope, orientation, stratification, rock exposure, and soil type. They include berms, mounds, hills, cliffs, valleys, rivers, and numerous other elements. Oceans and continents are the highest-order landforms.
=== Artificial features ===
==== Settlements ====
A settlement is a permanent or temporary community in which people live. Settlements range in components from a small number of dwellings grouped together to the largest of cities with surrounding urbanized areas. Other landscape features such as roads, enclosures, field systems, boundary banks and ditches, ponds, parks and woods, mills, manor houses, moats, and churches may be considered part of a settlement.
==== Administrative regions and other constructs ====
These include social constructions that are created to administer and organize the land, people, and other spatially-relevant resources. Examples are governmental units such as a state, cadastral land parcels, mining claims, zoning partitions of a city, and church parishes. There are also more informal social features, such as city neighbourhoods and other vernacular regions. These are purely conceptual entities established by edict or practice, although they may align with visible features (e.g. a river boundary), and may be subsequently manifested on the ground, such as by survey markers or fences.
==== Engineered constructs ====
Engineered geographic features include highways, bridges, airports, railroads, buildings, dams, and reservoirs, and are part of the anthroposphere because they are man-made geographic features.
=== Cartographic features ===

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Cartographic features are types of abstract geographical features, which appear on maps but not on the planet itself, even though they are located on the planet. For example, grid lines, latitudes, longitudes, the Equator, the prime meridian, and many types of boundary, are shown on maps of Earth, but do not physically exist. They are theoretical lines used for reference, navigation, and measurement.
== Features and Geographic Information ==
In GIS, maps, statistics, databases, and other information systems, a geographic feature is represented by a set of descriptors of its various characteristics. A common classification of those characteristics has emerged based on developments by Peuquet, Mennis, and others, including the following :
Identity, the fact that a feature is unique and distinct from all other features. This does not have an inherent description, but humans have created many systems for attempting to express identity, such as names and identification numbers/codes.
Existence, the fact that a feature exists in the world. At first, this may seem trivial, but complex situations are common, such as features that are proposed or planned, abstract concepts (e.g., the Equator), under construction, or that no longer exist.
Kind (also known as class, type, or category), one or more groups to which a feature belongs, typically focused on those that are most fundamental to its existence. It thus completes the sentence "This is a _________." These are generally in the form of common nouns (tree, dog, building, county, etc.), which may be isolated or part of a taxonomic hierarchy.
Relationships to other features. These may be inherent if they are crucial to the existence and identity of the feature, or incidental if they are not crucial, but "just happen to be." These may be of at least three types:
Spatial relations, those that can be visualized and measured in space. For example, the fact that the Potomac River is adjacent to Maryland is an inherent spatial relation because the river is part of the definition of the boundary of Maryland, but the overlap relation between Maryland and the Delmarva Peninsula is incidental, as each would exist unproblematically without the other.
Meronomic relations (also known as partonomy), in which a feature may exist as a part of a larger whole, or may exist as a collection of parts. For example, the relationship between Maryland and the United States is a meronomic relation; one is not just spatially within the boundaries of the other, but is a component part of the other that in part defines the existence of both.
Genealogical relations (also known as parent-child), which tie a feature to others that existed previously and created it (or from which it was formed by another agent), and in turn to any features it has created. For example, if a county were created by the subdivision of two existing counties, they would be considered its parents.
Location, a description of where the feature exists, often including the shape of its extent. While a feature has an inherent location, measuring it for the purpose of representation as data can be a complex process, such as requiring the invention of abstract spatial reference systems, and the necessary employment of cartographic generalization, including an expedient choice of dimension (e.g., a city could be represented as a region or as a point, depending on scale and need).
Attributes, characteristics of a feature other than location, often expressed as text or numbers; for example, the population of a city. In geography, the levels of measurement developed by Stanley Smith Stevens (and further extended by others) is a common system for understanding and using attribute data.
Time is fundamental to the representation of a feature, although it does not have independent temporal descriptions. Instead, expressions of time are attached to other characteristics, describing how they change (thus, they are analogous to adverbs in common discourse). Any of the above characteristics is mutable, with the possible exception of identity. For example, the lifespan of a feature could be considered as the temporal extent of its existence. The location of a city can change over time as annexations expand its extent. The resident population of a country changes frequently due to immigration, emigration, birth, and death.
The descriptions of features (i.e., the measured values of each of the above characteristics) are typically collected in Geographic databases, such as GIS datasets, based on a variety of data models and file formats, often based on the vector logical model.
== See also ==
Geographical field
Geographical location
Human geography
Landscape
Physical geography
Simple Features
== References ==

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Geographical segregation exists whenever the proportions of population rates of two or more populations are not homogeneous throughout a defined space. Populations can be considered any plant or animal species, human genders, followers of a certain religion, people of different nationalities, ethnic groups, etc.
In social geography segregation of ethnic groups, social classes and genders is often measured by the calculation of indices such as the index of dissimilarity. Different dimensions of segregation (or its contrary) are recognized: exposure, evenness, clustering, concentration, centralization, etc. More recent studies also highlight new local indices of segregation.
Geographical segregation is most often measured with individuals' place of residence, but increasing geographical data availability makes it now possible to compute segregation indexes using individuals' activity space, in whole or in part.
== Human geographical segregation ==
Segregation, as a broad concept, has appeared in all parts of the world where people exist—in different contexts and times it takes on different forms, shaped by the physical and human environments. The spatial concentration of population groups is not a new phenomenon. Since societies began to form there have been segregated inhabitants. Either segregated purposefully by force, or gradually over time, segregation was based on socio-economic, religious, educational, linguistic or ethnic grounds. Some groups choose to be segregated to strengthen social identity.
== Types ==
=== Legal segregation ===
Segregation can be caused by legal frameworks, such as in the extreme example of apartheid in South Africa, and even Jewish ghettoization in Germany in the 20th century. Segregation can also happen slowly, stimulated by increased land and housing prices in certain neighborhoods, resulting in segregation of rich and poor in many urban cities. Segregation can also be assigned arbitrarily. This can occur on a global scale, such as is seen in the Partition of India, instances in Ireland, and many other situations. Geographical boundaries were often put in place without much consideration for native peoples and natural geographic terrain and cultural limits that had long been in place.
In the United States, segregation was enforced through the law. Notably, the racial segregation between white and black racial populations in the American South during the late 1800s into the first half of the 20th century. These laws consisted of separating people of color from white people in public places, including movie theaters, restaurants, schools, shopping centers, etc. The legislations were commonly referred to as Jim Crow laws. Although these laws were abolished in the mid 1960’s the impacts are still present in American communities today. Represented through the significant gap in homeownership, income status, and education levels in communities of color versus majority white.
In apartheid South Africa, segregation was very much a legal concept. Enforced by the government, black and South-Africans of color were discriminated against, and forced to comply with apartheid. Some of the legislation passed dealt with physical segregation in schools, land tenure, geographic segregation and state repression. These were very clearly legislative, but also in the case of most white South Africans, a social construct as well.
Segregation can also be encouraged, using geographical boundaries, while not explicitly enforced. Public housing projects, especially in the United States, have been criticized for this. Putting cheap housing in poor black neighborhoods encouraged local African-Americans to stay in the area, keeping other richer areas white by not building public housing there. Current day, many communities within the United States are still segregated, due to the ongoing racial inequalities still present and self-segregation.

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=== Social segregation and gentrification ===
Segregation can also be caused by social factors that become evident as they happen, but are not necessarily government sanctioned. This could be things like informal ghettos, or simply rich neighborhoods. In terms of land capital, over time in a given area, humans will settle down and buy or take land. Some privileged people will acquire better land (that is, more arable, proximate to potential capital, more pleasing views). Demand for these nicer habitats drives up prices, and areas deemed "better" based solely on geography become inherently exclusionary in their population makeup.
West Point Grey, an area of Vancouver Canada, is in part rich because of the views offered of Downtown Vancouver, the Gulf Islands, and its location near the water and University of British Columbia. Wealthy people had the resources to pay for advantages, and subsequently drove up prices. Examples of this can be seen all over the world. Geographical segregation is not always defined by the sightline of places. It also occurs around certain structures, or simply in areas that are specifically developed with an income bracket in mind.
These social factors are commonly attributed to the impacts of gentrification. Gentrification is the process in which the makeup of a community is changed. These changes include racial identity, economic status, and level of education. Generally, gentrification occurs in communities that are low-income and a majority-minority population. It begins when affluent families, usually of white racial identity, move into these lower-income neighborhoods and invest their money into the community. These improvements to the community consist of reconstructing public transit, the businesses within downtown areas, and the houses in neighborhoods. This raises the overall investment value of the area, which increases the living costs. Which in turn, causes the original low-income residents to be displaced, due to the unaffordability. It can also create physical health issues for the original residents. As they are segregated in areas typically near factors or construction zones, exposing them to toxins. The Center for Disease Control and Prevention has issued that gentrification is a public health issue.
Another segregation term, the ghetto, has been used in many different contexts over time, generally meaning any physical part of a city predominantly occupied by any particular group of people. It implies that the group may be looked down upon and segregated purposefully. This does not mean that all ghettos are built up communities and buildings specifically for a segregation purpose, although many are. In the case of the United States, segregation of the African-American community was to a degree due to white flight out of the cities, rather than forcing African-Americans to live in the downtown cores.
=== Gated communities ===
Gated communities could be seen as a combination of both legal frameworks and social conventions regarding segregation. A gated community today is a controlled neighborhood, inhabited by people with common interests, such as safety, or class separation, but not necessarily of the same ethnicity or religion—it is distinct from an international community (in most cases). Gated communities are very controversial, as they can be seen as encouraging distinction and separation, and therefore superiority from those who do not live with the gates community.
=== Self-segregation ===
Self segregation is almost as common an occurrence as involuntary segregation is. Often, immigrants coming to a new and foreign country will band together for mutual benefit, and to keep a sense of community in the new country. These can be called ethnic enclaves and can be formed by any community or people group. Some well-known groups are Chinatowns, Little Italys and barrios. These localized phenomena also come in the form of ethnoburbs, which are essentially the same concept as an ethnic enclave, but specifically located in suburbs, rather than the traditional downtowns, where Chinatowns and Little Italys are usually based.
== References ==

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A geological event is a temporary and spatially heterogeneous and dynamic (diachronous) happening in Earth history that contributes to the transformation of Earth system and the formation of geological strata. Event stratigraphy was first proposed as a system for the recognition, study and correlation of the effects of important physical or biological events on the broader stratigraphical record.
Geological events range in time span by orders of magnitude, from seconds to millions of years, and in spatial scale from local to regional and, ultimately, global. In contrast to chronostratigraphic or geochronological units, that define the boundaries between periods, epochs and other units of the geologic time scale, complex dynamic diachronous changes are inherent to the event-stratigraphy paradigm. The lithostratigraphic or biostratigraphic boundaries that mark the onset and termination of geological events in the stratigraphic record may be diachronous, whereas those of formal chronostratigraphic or geochronologic units have basal boundaries that are isochronous.
Examples of geological events include a single footprint, an earthquake, a series of volcanic eruptions, the formation of mountains (orogenies), the Great Oxidation Event (GOE) of 2.4-2.0 billion years ago and the Great Ordovician Biodiversification Event (GOBE) ~500 Ma. The event paradigm is firmly embedded in Quaternary science, as the subdivision of quaternary time is based on the recognition of a succession of climatic events, principally glacial and interglacial cycles but also stadials and interstadials. Highly resolved stratigraphic sequences, such as those from ice cores, provide evidence of much shorter-term millennial-scale climatic events that are superimposed on these broad glacial cycles. Other short-term happenings, such as Dansgaard–Oeschger events and Heinrich events, are evident in ice-core sequences and deep-ocean sediment records, respectively. Some scientists have proposed that the Anthropocene is more consistent with the concept of a geological event than with a formal chronostratigraphic/geochronological unit, such as an epoch of geologic time.
== References ==

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The term geon (for geological eon) refers to large, geologic units of time.
Geologists traditionally subdivide Earth history into a hierarchy of named intervals: eons, eras, periods, etc. (e.g., the Jurassic Period of the Mesozoic Era). Historians subdivide the history of human activity into intervals that are comparatively much shorter. In both geological and historical scales, the divisions of equal rank are characteristically of unequal duration, and the identification of a particular interval is primarily based on its fossil, artifact, or cultural content (e.g., Carboniferous, Neolithic, Dark Ages, Ming Dynasty). Both scales are calibrated against numerical ages obtained
separately.
An alternative way of referring to the past is to use a scale with intervals of equal duration. We speak of a given decade, century, or millennium. For the enormously long geologic time frame, it is advantageous to use corresponding large, equal time intervals encompassing the events and processes that have shaped our planet. The development of mountain ranges, ocean basins, and continents takes tens to hundreds of millions of years, and large time units thus are convenient for discussing long-term trends. Astronomers use light years and parsecs to deal with huge distances, rather than kilometres. Geologists have geons to refer to large specified time intervals of Earth history. The geon scale is also applicable to other planets with different histories, and to the universe itself.
Two usages of geon have been introduced in geology:
A geon is a unit "...taken to represent either the span of the average geologic period, or the thickness of the average stratigraphic equivalent, a matter of 60,000,000 years, and 50,000 feet [~15 km] of clastic depositions" (Woodward, 1929). Utilizing the currently accepted value of 542 Ma (million years ago) for the beginning of the Cambrian Period, and using 11 geologic periods in the Phanerozoic Eon, an updated value for Woodward's geon would be about 49.4 million years. Usage in this sense is not current.
A geon is a specified 100-million-year interval of geologic time, counted backward from the present. The geon scale can be likened to a ladder, each interval between rungs representing 100 million years. Geons are named for the leftmost part of the number representing age. For example, the Earth formed about 4550 million years ago, an event that is assigned to Geon 45 (interval below rung 45). Rocks formed at 1851 Ma or 1800 Ma both belong to Geon 18. The extinction of the dinosaurs at the end of the Cretaceous Period (065 Ma) belongs to Geon 0. (Hofmann, 1990).
== References ==
Hofmann, H.J. (1990). "Precambrian time units and nomenclature - the geon concept". Geology. 18 (4): 340–341. Bibcode:1990Geo....18..340H. doi:10.1130/0091-7613(1990)018<0340:ptuant>2.3.co;2. Archived from the original on 2005-10-01.
Woodward, H.P. 1929, Standardization of geologic time-units. Pan-American Geologist, v. 51, p. 15-22.

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Geosophy is a concept introduced to geography by J.K. Wright in 1947. The word is a compound of ‘geo’ (Greek for earth) and ‘sophia’ (Greek for wisdom). Wright defined it thus:
Geosophy ... is the study of geographical knowledge from any or all points of view. It is to geography what historiography is to history; it deals with the nature and expression of geographical knowledge both past and present—with what Whittlesey has called ‘man’s sense of [terrestrial] space’. Thus it extends far beyond the core area of scientific geographical knowledge or of geographical knowledge as otherwise systematized by geographers. Taking into account the whole peripheral realm, it covers the geographical ideas, both true and false, of all manner of people—not only geographers, but farmers and fishermen, business executives and poets, novelists and painters, Bedouins and Hottentots—and for this reason it necessarily has to do in large degree with subjective conceptions.
THE CONCEPT OF GEOSPHY
Geosophy is the school of thought that asserts that earth cannot be studied independent of the people who live & experiences Earth.
The range of perception of the Earth is so varied & there are as many perception as people themselves, so, it is impossible to study the Earth independent of people who experiences it.
This concept reinforced the concept of cultural landscape of Carl 0. Sauer & Ratzel & also the work of vidals Genere-de-vie.
(Wright 1947)
This has been summarised as:
the study of the world as people conceive of and imagine it
(McGreevy 1987)
Belief systems as they relate to human interaction with the Earth's environments.
(attributed to Professor Innes Park 1995)
== Superstition ==
Geosophy is sometimes used as a synonym for the study of earth mysteries.
== See also ==
American Association of Geographers
Geopoetics
Technical geography
Quantitative geography
Qualitative geography
== References ==
Keighren, Innes M. “Geosophy, imagination, and terrae incognitae: exploring the intellectual history of John Kirtland Wright.” Journal of Historical Geography 31, no. 3 (2005): 546–62.
McGreevy, P. 1987 Imagining the future at Niagara Falls. Annals of the Association of American Geographers 77 (1):48–62
Wright, J.K. 1947. Terrae Incognitae: The Place of Imagination in Geography Annals of the Association of American Geographers 37: 1–15.

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Getting lost is the occurrence of a person or animal losing spatial reference. This situation consists of two elements: the feeling of disorientation and a spatial component. While getting lost, being lost or totally lost, etc. are popular expressions for someone in a desperate situation (perhaps not literally lost), getting lost is also a positive term for a goal some travellers have in exploring without a plan. Getting lost can also occur in metaphorical senses, such as being unable to follow a conversation.
== Process ==
Psychology and neuroscience help to understand the underlying processes which take place before, during and after getting lost. Getting lost is an aspect of behavioral geography, in which human wayfinding and cognitive and environmental factors play a role. For successful travel, it is necessary to be able to identify origin and destination, to determine turn angles, to identify segment lengths and directions of movement, to recognize on-route and distant landmarks. This information is required to plot a course designed to reach a destination (previously known or unknown) or to return to a home base after wandering. If a destination is known but is not directly connected by a path, road, or track to the origin, successful travel may involve search and exploration, spatial updating of one's location, finding familiar landmarks, recognition of segment length and sequencing, identification of a frame of reference. Human movement is often guided by external aids (cartographic maps, charts, compasses, pedometers, and the like).
Getting lost is particularly problematic for children (who have not yet developed tools and strategies for maintaining their bearings) and for the elderly, particularly those experiencing the onset of dementia. Such individuals "can get lost while trying to find their local shop – due to their diminishing memory they can forget where the shop is, or where they live and why they went out of their house in the first place". People experiencing dementia also get lost more easily in poor visibility conditions because the mind fails to appropriately fill in cues as to missing landmarks. Getting lost in unfamiliar terrain can lead even an adult with a healthy mind to panic and engage in unthinking behaviors that make the situation even worse. The tendency of the mind to seek patterns and familiar signs can contribute to this in two ways. First the lost person may mistake features of the terrain for markers that were seen before they became lost, creating a false sense of orientation that may lead the lost person to pursue routes that take them even further off course. Second, the lost person may mistake such features for markers that were seen after they became lost, creating a false sense that they have made a circle and returned to an earlier point of their effort to find their bearings. This may result from topographical disorientation, the inability to orient oneself in one's surroundings, sometimes as a result of focal brain damage. This disability may result from the inability to make use of selective spatial information (e.g., environmental landmarks) or to orient by means of specific cognitive strategies such as the ability to form a mental representation of the environment, also known as a cognitive map.
== Lost person behavior ==
Search and rescue teams have identified some behavioral patterns in people who get lost in wilderness settings, and they use those patterns to improve the likelihood of finding lost people. For example, lost people tend to follow linear features (e.g., a stream) and to go downhill.
== Historical occasions ==
There have been some historically notable instances of people getting lost and either being rescued or dying. George Shannon, the youngest adult member of the Lewis and Clark Expedition got lost on two occasions after being separated from the expedition. On August 26, 1804, he was sent to retrieve two pack horses; he was separated from the party for sixteen days and nearly starved, as he went without food for twelve days except for some grapes and rabbits. At first he thought he was behind the expedition, so he sped up thinking he could catch up. Then, getting hungry, he went downstream to look for a trading party he could stay with. Finally John Colter was sent to find him. The second time was on August 6, 1805, when the expedition was at the Three Forks. Shannon was dispatched up a fork the party had named Wisdom (the middle fork was named Jefferson and the placid fork, Philanthropy). He rejoined the party after three days by backtracking to the forks and following the trail of the others.
John Muir wrote in his journals of an occasion when a visiting artist named Billy Simms "went forth to sketch while I was among the glaciers, and got lost - was thirty-six hours without food". Mentally ailing Church of England mission priest Alexander Mackonochie died after getting lost on December 14, 1887, while walking in the Forest of Mamore, near Loch Leven, Scotland: the circumstances were later commemorated in a poem by William McGonagall. In September 2014, Soviet and Russian mathematician Alexey Chervonenkis got lost in Losiny Ostrov National Park; a later search operation found him dead near Mytishchi, a suburb of Moscow.
== In fiction and mythology ==
People are sometimes depicted in fiction and literature as getting lost, with substantial consequences. For example, due to "the physical structure of Rome, whose streets were notoriously labyrinthine", it has been observed that "getting lost in Rome was staple of travel narratives". The experience of getting lost is also a commonly reported theme of dreams.
In previous times, mythological explanations were given for getting lost and going astray. In the mythology of the British Isles, the culprit making someone get lost—being pixy-led, fairy-led or pouk-ledden as it is called—can be a fairy, Robin Goodfellow, Puck, Hob, a pixy or one of the gwyllion. In the mythology of Ireland, there are also places under fairy spells, leading to the same effect. They are called stray sod or foidin seachrain.
In German speaking Europe, someone getting lost could be attributed to be the fault of a variety of sprites (such as a Will-o'-the-wisp, a wood sprite, or the wild huntsman, the Mittagsweibchen ("noon-woman") or Rübezahl), of a witch or magic in general, or of mythical plants such as the Irrwurz. There are further places known called Irrfleck ("astray spot") or Irr-Revier ("astray district") where people go astray.
Getting lost in the bush has been identified as an enduring trope of Australian literature, often featuring lost children.
== References ==
== Further reading ==
Koester, Robert J. (2008). Lost Person Behavior: A search and rescue guide on where to look for land, air, and water. Charlottesville, VA: DbS Productions. ISBN 9781879471399. OCLC 213479933.
== External links ==
Media related to Getting lost at Wikimedia Commons

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This glossary gives translations of Hebrew terms commonly found as components in Hebrew toponyms.
== B ==
Be'er Beer Be'erot (plural)
בְּאֵר, wiktionary:באר, 'well'; plural בְּאֵרוֹת
All pages with titles beginning with Beer
All pages with titles beginning with Be'er
All pages with titles beginning with Be'erot
BeitBayit (sometimes)BethBet
בֵּית, wiktionary:בית, 'house'
All pages with titles beginning with Beit
All pages with titles beginning with Bayit
All pages with titles beginning with Beth
All pages with titles beginning with Bet
== E ==
Ein'En
עַיִן, wiktionary:עין, 'spring, fountain'
All pages with titles beginning with Ein
All pages with titles beginning with 'En
Emek
עֵמֶק, wiktionary:עמק, 'valley'
All pages with titles beginning with Emek
== G ==
Gan
גַּן, wiktionary:גן, 'garden'
All pages with titles containing Gan
Giv'atGivatGivatayim (dual)Giv'ot (plural)
גִּבְעַת, wiktionary:גבעה, 'hill'
All pages with titles beginning with Givat
All pages with titles beginning with Giv'at
All pages with titles beginning with Giv'ot
== H ==
Har
הַר, wiktionary:הר, 'mountain'
All pages with titles beginning with Har
== I ==
Illit
עילית, wiktionary:עילית, 'upper'
All pages with titles containing Illit
== K ==
Kerem
כֶּרֶם, wiktionary:כרם, 'vineyard'
All pages with titles beginning with Kerem
Kfar
כְּפַר, wiktionary:כפר, 'village'
All pages with titles beginning with Kfar
KiryatQiryat
קִרְיַת, wiktionary:קריה, 'town'
All pages with titles beginning with Kiryat
All pages with titles beginning with Qiryat
== M ==
Ma'ayanMa'yan
מעיין, wiktionary:מעיין, 'spring, fountain'
All pages with titles beginning with Ma'ayan
All pages with titles beginning with Ma'yan
Mishmar
מִשְׁמַר, wiktionary:משמר, 'guard'
All pages with titles beginning with Mishmar
== N ==
Nahal
נַחַל, wiktionary:נחל, stream, wadi, Biblical Hebrew: 'valley'
All pages with titles beginning with Nahal
All pages with titles beginning with Nachal
Neve Neot (plural)
נְוֵה, נוה, in this context: '(place of) residence, abode, oasis'; plural נאות
All pages with titles beginning with Neve
All pages with titles beginning with Neot
== Q ==
Qiryat: see Kiryat
== R ==
Ramat
רָמַת, wiktionary:רמה, 'heights, highlands'; plural Ramot
All pages with titles beginning with Ramat
Ramot
רָמוֹת, 'heights, highlands'; plural of Ramat
All pages with titles beginning with Ramot
Rosh
רֹאשׁ, wiktionary:ראש, 'head'
All pages with titles beginning with Rosh
== T ==
Tel
תֵל, wiktionary:תל, 'mound (tell), hill', often in names of archaeological sites
All pages with titles beginning with Tel
TzurTsur
צוּר, wiktionary:צור, 'rock, cliff'
All pages with titles beginning with Tzur
All pages with titles beginning with Tsur
== See also ==
List of Hebrew place names
Hebraization of Palestinian place names
== Further reading ==
M. E. J. Richardson, "Hebrew Toponyms", Tyndale Bulletin Vol. 20, Issue 1, 1969, doi:10.53751/001c.30678
Joseph Jacobs, Place-names, Jewish Encyclopedia
Yoel Elitzur, "Toponyms in the Land of Israel", In: Encyclopedia of Hebrew Language and Linguistics, 2013, vol. 3, pp. 779-778

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This glossary of geology is a list of definitions of terms and concepts relevant to geology, its sub-disciplines, and related fields. For other terms related to the Earth sciences, see Glossary of geography terms (disambiguation).
== A ==
abiotic
Non-living chemical or physical component of the environment affecting living organisms and the functioning of ecosystems.
abyssal plain
A flat or very gently sloping area on the floor of a deep ocean basin.
absolute dating
The process of determining a specific date (in years or some other unit of time) for an archaeological, geological or paleontological site or artifact.
accident
A sudden discontinuity of ground, such as a fault of great thickness, bed or lentil of unstable ground.
accretion
A process by which material is added to a tectonic plate or landmass.
achnelith
A small, glassy volcanic bomb, sphere, dumbbell, or droplet-shaped stone resulting from very liquid magma.
acid rock
The groups ultrabasic, basic, intermediate and acid constitute a series with progressively increasing SiO2 content.
aftershock
A small earthquake that follows a main shock.
agglomerate
An indurated rock built of large angular rock fragments embedded in an ashy matrix and resulting from explosive volcanic activity. Occurs typically in volcanic vents.
aggregate
A mass consisting of rock or mineral fragments.
albite
The end member of the plagioclase group of minerals, ideally consisting of silicates of sodium and aluminium, but commonly containing small quantities of potash and lime in addition. Compare barbierite.
alkaline
A highly basic substance that dissolves in water.
alkaline rock
A type of rock characterized by a high content of Na2O and K2O relative to the other oxides. They occur throughout the range from ultrabasic to acid, but have their strongest expression in the acid-intermediate part of the range.
allochthon
A fossil, sediment, or rock that was formed elsewhere and later transported into the location where it is presently found, usually by low angle thrust faulting. An object of this type is referred to as allochthonous. Contrast autochthon.
alluvial fan
A fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain.
alluvium
Soil or sediments deposited by a river or other running water.
amber
Fossilized resin or tree sap that is appreciated for its vivid colour, usually reddish-orange to gold or yellow.
amphibole
An important group of dark-coloured, rock-forming silicate minerals, including hornblende, the commonest.
amphibolite
A crystalline, coarse-grained rock, containing amphibole as an essential constituent, together with feldspar and frequently garnet. Like hornblende schist, amphibolite is formed by regional metamorphism of basic igneous rocks, but is not foliated.
amygdaloidal
Amygdules or amygdales form when the gas bubbles or vesicles in volcanic lava (or other extrusive igneous rocks) are infilled with a secondary mineral such as calcite, quartz, chlorite or one of the zeolites. Rocks containing amygdules can be described as amygdaloidal.
anatexis
Melting of pre-existing rock. Compare metatexis, diatexis, and syntexis.
andalusite
One of several crystalline forms of aluminium silicate; a characteristic product of the contact metamorphism of argillaceous rocks.
andesite
Fine-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar with the rest being ferromagnesian minerals.
angular unconformity
An unconformity in which younger strata overlie an erosion surface of tilted or folded layered rock.
anorthite
Also called Indianite.
A mineral from the lime-rich end of the plagioclase group of minerals. Anorthites are usually silicates of calcium and aluminium occurring in some basic igneous rocks, typically those produced by the contact metamorphism of impure calcareous sediments.
anticline
An arched fold in which the layers usually dip away from the fold axis. Contrast syncline.
aphanic
Having the texture of carbonate sedimentary rocks characterized by individual crystals or clastic grains less than 0.01 mm in diameter.
aphanitic
Said of the texture of igneous rock in which the crystalline components are not distinguishable by the naked eye. Both microcrystalline and cryptocrystalline textures are included.
aplogranite
A light-coloured rock of granitic texture consisting mainly of alkali feldspar and quartz, with subordinate biotite; muscovite may be present.
aquifer
A body of saturated rock or sediment through which water can move readily.
aragonite sea
Contains aragonite and high-magnesium calcite as the primary inorganic carbonate precipitates.
Archean Eon
The oldest eon of the Earth's history.
archipelago
A chain or cluster of islands.
arenaceous
Sediments consisting essentially of sand grains; that is, of quartz and rock fragments down to 0.005mm in size. Conglomerates, sandstones, grits and siltstones fall into this category. Particle size 2mm to 1/16mm.
arenite
1. A general term for any consolidated sedimentary rock composed of sand-sized fragments.
2. “Clean” sandstone, well-sorted, less than 10% argillaceous matrix. Opposite to Wacke.
arenitic
Pertaining to, having the quality of, or resembling sandstone.
arkose
An arenaceous sedimentary rock. Like sandstone in its general character but containing feldspar to at least 10%. Formed by the disintegration of the acid igneous rocks and gneisses.
argillaceous
Sedimentary rocks of the clay grade, i.e. composed of minute mineral fragments and crystals less than 0.005 mm in diameter, as well as large amounts of colloidal material. Apart from finely divided detrital matter, they consist of the so-called clay minerals, such as montmorillonite, kaolinite, gibbsite and diaspore. Siltstones, mudstones, shales, clays, etc. may all be referred to as argillaceous.
ash
Fragments less than 2 mm (0.079 in) in diameter of pulverized rock, minerals and volcanic glass, created during volcanic eruptions.
asphalt
A sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits.
assembled gem
Also called a composite gem.
asthenosphere
A region of the Earth's outer shell beneath the lithosphere. The asthenosphere is of indeterminate thickness and behaves plastically.
augite
A complex aluminous silicate of calcium, iron and magnesium, crystallising in the monoclinic system, and occurring in many igneous rocks, particularly those of basic composition. It is an essential component of basalt, dolerite and gabbro.
aureole
A zone surrounding an igneous intrusion in which country rock shows effects of contact metamorphism.

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autochthon
A fossil, sediment, or rock that was formed or produced in the location where it is now found. The term is widely applied to a coal or peat that originated at the place where the plants comprising it grew and decayed and to rocks that have not been displaced by overthrust faulting. An object of this type is referred to as autochthonous. Contrast allochthon.
== B ==
bajada
A series of coalescing alluvial fans along a mountain front.
banded iron formation
A distinctive type of rock often found in primordial sedimentary rocks.
basalt
A fine-grained, mafic igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium-rich plagioclase feldspar.
basement rock
The thick foundation of ancient, and oldest metamorphic and igneous rock that forms the crust of continents, often in the form of granite.
basic rock
Igneous rock with low silica content (<54%). The groups ultrabasic, basic, intermediate, and acid constitute a series with progressively increasing SiO2 content.
basin
A landform scooped out by water erosion.
Basin and Range Province
A particular topography covering much of the southwestern United States and northwestern Mexico that is typified by elongate north-south trending arid valleys bounded by mountain ranges which also bound adjacent valleys.
batholith
A large discordant pluton with an outcropping area greater than 100 square kilometres (39 sq mi).
bedrock
Native consolidated rock underlying the loose rock or soil surface of the Earth.
Before Present (BP)
bentonite
Swelling clay minerals of the smectite group with many industrial applications (drilling mud, expansive backfill materials…). The name bentonite is inherited from Fort Benton in Wyoming where large swelling clay deposits exist. See also smectite and montmorillonite.
bioerosion
The erosion of hard ocean substrates by living organisms through various biological mechanisms.
biogenic
Of biological origin – Produced by the present or past activity of living organisms, or by a biological process.
bioherm
Landform of organic sedimentary rock enclosed or surrounded by rock of different origin.
biostratigraphy
A branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.
biostratinomy
The study of the processes that take place after an organism dies but before its final burial.
biostrome
A distinctly bedded or broadly lenticular sedimentary rock landform.
biotic
Of biological origin – Produced by the present or past activity of living organisms, or by a biological process.
biotite
A form of black mica widely distributed in igneous rocks (particularly in granites) as lustrous black crystals, with a singularly perfect cleavage. In composition it is a complex silicate, chiefly of iron and magnesium, together with potassium and hydroxyl.
bioturbation
The displacement and mixing of sediment particles by benthic fauna (animals) or flora (plants).
blueschist
A rock that forms by the metamorphism of basalt or rocks of similar composition at high pressures and low temperatures, approximately corresponding to a depth of to and a temperature of to.
boudin
A structure formed by extension, in which a rigid tabular body such as a bed of sandstone is stretched and deformed amidst less competent beds. See also boudinage.
boulder
Bowen's reaction series
The sequence in which minerals crystallize from a cooling basaltic magma.
brackish
Water with a salinity higher than freshwater but lower than seawater.
breadcrust bomb
A rounded, smooth-surfaced volcanic bomb with a cracked surface resembling a cracked crust of bread, hence the name.
breccia
A coarse-grained clastic rock consisting largely of angular fragments of existing rocks.
buckling
A failure mode of a rock subjected to high compressive stresses, where the actual compressive stress at the point of failure is less than the ultimate compressive stresses that the material is capable of withstanding. Typically, folding is thought to occur by simple buckling of a planar surface and its confining volume. The volume change is accommodated by layer parallel shortening the volume, which grows in thickness.
== C ==
calcareous
Formed from or containing a high proportion of calcium carbonate in the form of calcite or aragonite, used of a sediment, sedimentary rock, or soil type.
calcite
A mineral that is the crystalline form of calcium carbonate (CaCO3), showing trigonal symmetry and a great variety of mineral habits. It is one of the commonest of minerals in association with both igneous and sedimentary rocks.
calcite sea
A body of water in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate.
calcrete
1. A conglomerate of surficial sand and gravel cemented by calcium carbonate precipitated from solution.
2. A calcareous duricrust.
caldera
A volcanic feature formed by the collapse of land following a volcanic eruption.
Cambrian
The earliest geologic period of the Paleozoic Era, lasting from 541.0 ± 1.0 to 485.4 ± 1.9 million years ago and succeeded by the Ordovician.
carbon film
A type of fossil or preservation.
carbonate
A salt or ester of carbonic acid.
carbonate hardgrounds
Surfaces of synsedimentarily-cemented carbonate layers that have been exposed on the seafloor.
casting
The process which occurs when a liquid fills a cavity and then solidifies. If the cavity originated from the decomposition of dead organisms, casting may result in the formation of fossils.
Cenozoic Era
The most recent of the geological eras, which followed the Mesozoic Era.
chalk
A soft, white, porous sedimentary rock, a form of limestone composed of calcite coccolith plates.
chert
A fine-grained, silica-rich, microcrystalline, cryptocrystalline or microfibrous sedimentary rock that sometimes contains small fossils.
chlorite
Any of a set of allied non-swelling 2:1 (TOT) clay minerals which may be regarded as hydrated silicates of aluminium, iron, and magnesium. Their non-accessible interlayer is filled by a brucite bridge (Mg(OH)2, or sometimes Fe(OH)2). They crystallise in the monoclinic system and are green in colour. They occur as alteration products of such minerals as biotite and hornblende, and also in schistose rocks.
clast
Any individual constituent grain or fragment of a sediment or rock produced by mechanical weathering of a rock mass.
clastic rocks
Mechanically redeposited remains of eroded older rocks; i.e. rocks formed of fragments, or clasts, of pre-existing rocks.
clay

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cleavage
The tendency of a rock to break along preferred planes of weakness, caused by the development of a planar fabric as a result of deformation.
cobble
coccolith
An individual plate of calcium carbonate formed by coccolithophores which are arranged around them in a so-called coccosphere.
coccolithophore
Also called a coccolithophorid.
A type of microfossil of single-celled algae, protists and phytoplankton belonging to the division of haptophytes. These fossils are distinguished by special calcium carbonate plates called coccoliths.
compaction
The process by which a newly deposited sediment decreases its porosity and progressively expels its original pore water due to the effects of loading. This forms part of the process of lithification.
compression
The process by which rocks shorten or decrease in volume when exposed to certain forces.
conchoidal
A type of fracture that results in smoothly curved surface faces.
concretion
A volume of sedimentary rock in which a mineral cement fills the porosity (i.e. the spaces between the sediment grains). Not to be confused with nodule.
conglomerate
Any type of rock consisting of individual stones that have become cemented together.
contact metamorphism
Metamorphism due to the local heating of rocks by the intrusion of magma nearby.
continental crust
The layer of granitic, sedimentary, and metamorphic rocks which form the parts of the Earth's crust that comprise the continents, and the areas of shallow seabed close to their shores (known as continental shelves).
continental margin
Zone of the ocean floor, separating the thin oceanic crust from thicker continental crust.
continental shelf
Extended perimeter of a continent and its associated coastal plain, which is covered, during interglacial periods (such as the current epoch), by gulfs, and relatively shallow seas known as shelf seas.
convergent boundary
The boundary between two tectonic plates that are moving toward each other. Contrast divergent boundary.
copal
A type of resin produced by plant or tree secretions, particularly identified with the forms of aromatic tree resins used by the cultures of pre-Columbian Mesoamerica as a ceremonially burned incense, as well as for a number of other purposes.
coprolite
A fossilized specimen of human or animal dung.
cordierite
A silicate of aluminium, iron and magnesium with water, which crystallises in the orthorhombic system and occurs mainly in metamorphic rocks.
core
The innermost layer(s) of a planet, referring especially to the Earth's core.
corestone
An ellipsoidal or broadly rectangular joint block of granite formed by subsurface weathering in the same manner as a tor but entirely separated from bedrock.
country rock
The rock native to an area, as opposed to rock that formed elsewhere and was later transported to the area.
craton
An old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for at least 500 million years.
cross-bedding
An inclined sedimentary structure in a horizontal unit of rock. Such tilted structures indicate the type of depositional environment, not post-depositional deformation.
crude oil
A liquid mixture of naturally occurring hydrocarbons.
crust
The outermost solid layer of a planet or moon, referring especially to the Earth's crust.
cryptocrystalline
crystal
crystal habit
crystallinity
== D ==
dacite
An igneous, volcanic rock with a high iron content. It is an extrusive rock of the same general composition as andesite, but a less calcic feldspar. Synonymous with quartz andesite.
daughter product
Any distinct isotope produced by the radioactive decay of an atomic nucleus.
delta
A landform where the mouth of a river flows into an ocean, sea, desert, estuary, lake or another river.
degradation
The lowering of a fluvial surface, such as a stream bed or floodplain, through erosional processes.
dendrite
A crystal that develops with a typical multi-branching tree-like form.
denudation
The lowering of the earth's surface through chemical and physical weathering.
deposition
The geological process by which material is added to a landform or landmass.
detachment fault
A major fault in a mountain belt above which rocks have been intensely folded or faulted.
diagenesis
The process of chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering) and metamorphism.
diamictite
A comprehensive non-generic term for a non-sorted or poorly sorted non-calcareous terrigenous sedimentary rock that contains a wide range of particle sizes such as rock with sand or larger particles in a muddy matrix.
diapir
A type of intrusion in which a more mobile and ductilely deformable material is forced into brittle overlying rocks; a dome or anticlinal fold of the overlaying rocks which has been ruptured by the squeezing out of the plastic core material.
diatomite
A soft, chalk-like sedimentary rock that is easily crumbled into a fine white to off-white powder.
diopside
A monoclinic pyroxene, ideally consisting of silicate of calcium and magnesium, but commonly containing a variable content of FeSi2O6 in addition, and then strictly known as ferriferous diopside.
diorite
A grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene.
dike
Also spelled dyke.
A type of sheet intrusion referring to any geologic body that cuts discordantly across. A form of minor intrusion injected into the crust during its subjection to tension, the dyke being thin with parallel sides, and maintaining a constant direction in some cases for long distances. Some are more resistant to weathering than the surrounding rock and stand up like walls, while others weather faster and form long narrow depressions.
dip slope
A geological formation often created by erosion of tilted strata.
disconformity
A surface that represents missing rock strata but beds above and below that surface are parallel to one another.
divergent boundary
The boundary separating two tectonic plates that are moving away from each other. Contrast convergent boundary.
dolomite
A sedimentary carbonate rock and mineral, both composed of crystalline calcium magnesium carbonate CaMg(CO3)2.

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dolerite
1. A basic igneous rock of medium grain size, occurring as minor intrusions or in the central parts of thick lava flows.
2. A dark-coloured, basic, igneous rock, composed essentially of pyroxene and a triclinic feldspar with magnetic iron. Considered by some authors to be equivalent to a coarse-grained basalt.
3. A dark, crystalline, igneous rock, chiefly pyroxene with labradorite.
4. Coarse-grained basalt.
5. Diabase.
6. Any dark igneous rock composed chiefly of silicates of iron and magnesium with some feldspar.
dome
A geological formation consisting of symmetrical anticlines that intersect each other at their respective apices.
drill core
A drill specifically designed to remove a cylinder of material, much like a hole saw.
drumlin
An elongated, whale-shaped hill formed by glacial action.
dunite
An ultrabasic plutonic rock in which the mafic material is almost entirely olivine, with accessory chromite almost always present. Feldspar mainly plagioclase. See also peridotite.
duricrust
A general term for hard crust existing as a layer in or on the surface of the upper horizons of a soil in semi-arid climates. Duricrust is formed by the accumulation of solid minerals deposited by water moving upwards by capillary action and evaporating in the dry season. Compare hardpan.
== E ==
earthquake
eclogite
A generally coarse- to medium-grained pyroxene in which are set red garnets. The colour is pistachio green when fresh, but mottled with red when weathered.
Eemian transgression
The portion of the Late Pleistocene spanning the period between 120 Ka and 8m before present.
eonThe largest unit of geologic time.
epicenter
The point on the Earth's surface that is directly above the hypocenter or focus at which an earthquake or underground explosion originates.
epidiorite
Any of a set of altered gabbroic and doleritic rocks in which the original pyroxene has been replaced by fibrous amphibole. The rock may be regarded as a first step in the conversion by dynamothermal metamorphism of a basic igneous rock into a green schist.
epirogenetic
The simultaneous rising and falling movements of continents, maintaining isostasy.
epoch
A division of the standard geologic time scale subordinate to periods. An example is the Pleistocene Epoch of the Quaternary Period.
erosion
The displacement of solids (sediment, soil, rock and other particles) usually by the agents of currents such as wind, water, or ice by downward or down-slope movement in response to gravity or by living organisms (in the case of bioerosion).
erratic
A piece of rock that deviates from the size and type of rock native to the area in which it rests. Erratics usually occur as stones ranging in size from pebbles to large boulders which were transported by glacial ice, which upon melting left them stranded far from their original source. The name "erratic" is based on the errant location of these boulders.
escarpment
A transition zone between different physiogeographic provinces that involves an elevation differential, characterized by a cliff or steep slope.
esker
A long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North America. Eskers are frequently several miles in length and, because of their peculiar uniform shape, somewhat resemble railroad embankments.
estuary
A semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea.
eugeosyncline
A geosyncline in which volcanism is associated with clastic sedimentation; the volcanic part of an orthosyncline located away from the craton.
euhedral
Bounded by the crystal faces peculiar to the species, used of minerals. Synonymous with idiomorphic.
eustatic movements
Changes of sea level, constant over wide areas, due to alterations in the volume of the oceans resulting from the formation or melting of ice caps.
evaporite
Any of a diverse set of water-soluble mineral sediments that result from the evaporation of bodies of surface water.
exfoliation
The stripping of concentric rock slabs from the outer surface of a rock mass.
extension
Strain involving an increase in length. Extension can cause thinning and faulting.
extrusive
A mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff.
== F ==
facies
The sum of the lithological and faunal characters of a sediment is its facies. Lithological facies involves composition, grain size, texture, colour, as well as such mass characteristics as current bedding, nature of stratification, ripple marks, etc. Similarly, metamorphic facies involves the degree of crystallisation and the mineral assemblage in a group of metamorphic rocks.
fanning
Rock deformation related to shear stress.
fault
A discrete planar rock fracture which shows evidence of a displacement (the throw of the fault). A fault is a discrete surface.
fault zone
The zone where exist different discrete fault planes.
feldspar
Any of a set of the most common minerals in the Earth's crust. All feldspars contain silicon, aluminium, and oxygen and may contain potassium, calcium and sodium.
fels
A massive metamorphic rock lacking schistosity or foliation.
felsic
Silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Light minerals (quartz and feldspar) greater than 60% - acid. [Granite (Rhyolite), Adamellite (Rhyo-dacite), Granodiorite (Dacite)]. The term is a mnemonic adjective for igneous rocks having light-coloured minerals in their mode, from "feldspar" and "silica". Contrast mafic.
ferricrete
A conglomerate consisting of surficial sand and gravel cemented into a hard mass by iron oxide derived from oxidation of percolating solution of iron salts. A ferruginous duricrust.
ferromagnesian mineral
Any iron/magnesium-bearing mineral, such as augite, hornblende, olivine, or biotite.
fission track dating
A method that uses tracks that are visible under the microscope to date minerals.
Flandrian transgression
fold
A stack of originally flat and planar surfaces, such as sedimentary strata, which have become bent or curved as a result of plastic (i.e. permanent) deformation.
foliation
The parallel alignment of textural and structural features of a rock.

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fossil
Any mineralized or otherwise preserved remains or traces (such as footprints) of animals, plants, or other once-living organisms.
fossiliferous
Bearing or being composed of fossils in rocks or strata.
fossilization
fracture
Any crack or discontinuity. In its geological definition, it is only used when no displacement can be distinguished.
fumarole
A vent in the Earth's surface from which hot gases and vapors are emitted.
== G ==
Ga
A non-standard but widely used abbreviation for one billion (1,000,000,000) years, using the metric prefix G (for "Giga") to indicate a quantity of one billion. When not otherwise qualified, it usually indicates 1,000,000,000 years Before Present (or 1,000,000,000 years ago).
gabbro
A dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt.
garnet
gastrolith
A rock which is or was once held inside the digestive tract of a living animal.
gemology
Also spelled gemmology.
The branch of geology and mineralogy that studies natural and artificial gemstones.
gemstone
Also called a gem, fine gem, jewel, precious stone, or semi-precious stone.
geogenic
Of geologic origin – Resulting from naturally occurring geological processes.
geological map
A special-purpose map made to show geological features.
geological time scale
Also geologic time scale.
geology
geosyncline
A mobile down-warping of the Earth's crust, either elongate or basin-like, measured in scores of kilometres, which is subsiding as sedimentary and volcanic rocks accumulate to thicknesses of thousands of metres.
glass
Amorphous (non-crystalline) hard and brittle solid such as soda-lime glass.
glauconite
A green-coloured, hydrated silicate mineral of potassium and iron that forms on submerged banks. Its occurrence in sands and sandstones is considered an indication of accumulation under marine conditions.
gneiss
A coarse-grained, pale-coloured gneissose rock, containing abundant feldspar with quartz, mica, hornblende, and garnet.
Gondwanaland
The southern part of the supercontinent of Pangaea which eventually separated to form present-day South America, Africa, India, Australia and Antarctica.
graben
A depressed block of the Earth's crust bordered by parallel faults.
granite
A coarse-grained, often porphyritic, intrusive, felsic, igneous rock containing megascopic quartz, averaging 25%, much feldspar (orthoclase, microcline, sodic plagioclase) and mica or other coloured minerals. Rhyolite is the volcanic equivalent.
granitoid
Any granite-like rock, including granodiorite, diorite, monzonite, and granite itself, among others.
granoblastic
An arrangement of mineral grains in a rock of metamorphic origin similar to that of a normal granite, but produced by recrystallisation in the solid and not by crystallisation from a molten condition.
granodiorite
An intrusive, felsic, igneous rock similar to granite but containing more plagioclase than potassium feldspar. Dacite is the volcanic equivalent.
granulometry
Statistical distribution of the size of individual sediment grains, or lithified particles in clastic rocks.
gravel
graywacke
Also spelled greywacke.
A variety of sandstone generally characterized by its hardness, dark colour, and poorly sorted, angular grains of quartz, feldspar, and small rock fragments (lithic fragments) set in a compact, clay-fine matrix.
greenstone
An omnibus term lacking precision and applied indiscriminately to basic and intermediate igneous rocks of Lower Paleozoic age in which much chlorite has been produced at the expense of the original coloured minerals, staining the rocks green.
grus
Freshly eroded, angular grains of quartz and feldspar derived from a granitoid.
== H ==
habit
See crystal habit.
half-life
The time it takes for a given amount of a radioactive isotope to be reduced by one-half.
hardpan
hemicrystalline
Having the properties of certain rocks of igneous origin which contain some interstitial glass in addition to crystalline minerals. Contrast holocrystalline.
hinge
The zone of maximum curvature of a fold.
hinge line
A line joining the points of maximum curvature along the hinge of a fold.
holocrystalline
Having the properties of those igneous rocks in which all of the components are crystalline; glass is absent. Contrast hemicrystalline.
hornblende
An important rock-forming mineral of complex composition, essentially a silicate of calcium, magnesium and iron, with smaller amounts of potash, soda and hydroxyl. Hornblende crystallises in the monoclinic system and occurs as black crystals or grains in many different types of igneous and metamorphic rocks, including hornblende-granite, syenite, diorite, andesite, hornblende-schist, and amphibole.
hornfels
A hard, compact, fine-textured contact-altered argillaceous rock that breaks into splintery fragments.
horst
A raised fault block bounded by normal faults.
hot spring
A natural spring resulting from the emergence of geothermally heated groundwater from beneath the Earth's crust.
hydrothermal
Pertaining to the actions or products of heated water.
hydrothermal vent
A fissure in a planet's surface from which geothermally heated water emerges.
hypersaline
Having a saltiness or dissolved salt content greater than that of seawater.
== I ==
ichnology
The study of traces of organismal behavior.
idiomorphic
Bounded by the crystal faces peculiar to the species, used of minerals. Synonymous with euhedral.
igneous rock
A type of rock formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.
ignimbrite
Fine-grained to aphanitic, buff to dark brown compact rock with parallel streaks or lenticles of black glass, produced by violently explosive volcanoes.
ilmenite
An oxide of iron and titanium, crystallising in the trigonal system; a widespread accessory mineral in igneous rocks, especially those of basic composition.
illite
Non-swelling clay mineral with a three layers 2:1 (TOT) structure. Its interlayers contain no water and anhydrous K+ cations responsible for their total collapse. Water and cations diffusion is not possible in these collapsed interlayers. The name "illite" is inherited from the state of Illinois where natural non-swelling clay deposits exist.
indurated
Made hard (by heat or compaction).
interbeddedbeds (layers) of rock lying between or alternating with beds of a different kind of rock.
intrusionbody of igneous rock that has crystallized from molten magma below the surface of the Earth.
island arc
A chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma.
isomorphic
Two crystals that have similar shapes and sizes, usually through the angles.
isotope
different forms of an element each having different atomic mass (mass number).
== J ==

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joint
A discrete discontinuity surface without evidence of displacement. See also diaclase or bedding.
Jurassic
A major unit of the geologic timescale that extended from about 199.6 ± 0.6 Ma (million years ago) to 145.4 ± 4.0 Ma, between the end of the Triassic and the beginning of the Cretaceous.
== K ==
Ka
A non-standard but widely used abbreviation for one thousand (1,000) years, using the metric prefix K (for "Kilo") to indicate a quantity of one thousand. When not otherwise qualified, it usually indicates 1,000 years Before Present (or 1,000 years ago).
kame
An irregularly shaped hill or mound composed of sand, gravel and till that accumulates in a depression on a retreating glacier and is then deposited on the land surface with further melting of the glacier.
kaolinite
A finely crystalline form of hydrated aluminium silicate occurring as minute monoclinic flaky crystals with a perfect basal cleavage, resulting mainly from the alteration of feldspars under conditions of hydrothermal or pneumatolytic metamorphism.
karst
A distinct type of landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. Karst topography is usually characterised by closed depressions or sinkholes, caves and underground drainage.
kettle
A fluvioglacial landform occurring as the result of blocks of ice calving from the front of a receding glacier and becoming partially to wholly buried by glacial outwash.
kink
A tight curl, twist, or bend in a rock band. See also folding and buckling.
kink band
An asymmetric, linear zone of deformation characterised by a tight curled, twisted, or bended rock band. Kink bands may also occur as conjugated sets.
kyanite
A silicate of aluminium which crystallises in the triclinic system. It usually occurs as long-bladed crystals, blue in colour, in metamorphic rocks.
== L ==
lacuna
A time-stratigraphic unit representing the gap in the stratigraphic record. Specifically the missing interval at an unconformity, representing the interpreted space-time value of both hiatus (period of non-deposition), and degradation vacuity (period of erosion).
lamprophyre
Igneous rocks usually occurring as dykes intimately related to larger intrusive bodies; characterised by abnormally high contents of coloured silicates, such as biotite, hornblende and augite, and a correspondingly small amount of feldspar, some being feldspar-free.
large igneous province
Massive volcanic formation resulting from flood basalt eruptions.
lava
Molten rock expelled by a volcano during an eruption.
leucocratic
A term used to denote a light colour in igneous rocks, due to a high content of felsic minerals and a correspondingly small amount of dark, heavy silicates.
limestone
A sedimentary rock composed largely of the mineral calcite (calcium carbonate: CaCO3).
liquefaction
Soil liquefaction describes the behavior of soils that, when loaded, suddenly suffer a transition from a solid state to a liquefied state, or having the consistency of a heavy liquid.
lithic fragment
Also simply called a lithic.
A sand-sized grain that is made up of smaller than sand-sized grains, e.g. a shale fragment or basalt fragment in a sandstone.
lithification
The process by which sediments compact under pressure, expel connate fluids, and gradually become solid rock.
lithology
A description of the physical characteristics of a rock unit visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition.
lithosphere
The rigid, outermost rocky shell of a terrestrial planet or natural satellite. The Earth's lithosphere is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of up to thousands of years or more.
lithotype
Specific types of rock classified according to the standards of lithology.
loess
A fine, silty, pale yellow or buff-coloured, windblown (eolian) type of unconsolidated deposit.
lustre
Also spelled luster.
== M ==
Ma
A non-standard but widely used abbreviation for one million (1,000,000) years, using the metric prefix M (for "Mega") to indicate a quantity of one million. When not otherwise qualified, it usually indicates 1,000,000 years Before Present (or 1,000,000 years ago).
mafic
A silicate mineral or rock that is rich in magnesium and iron. A mnemonic term for the ferromagnesian and other non-felsic minerals actually present in an igneous rock rich in dark (ferromagnesian) minerals (greater than 60% by volume). Basic [alkali gabbro (alkali basalt), syeno-gabbro (trachybasalt), gabbro (basalt and dolerite)].
magma
Molten rock that sometimes forms beneath the surface of the Earth (or other terrestrial planets) and often collects in a magma chamber.
magnetite
An oxide of iron which crystallises in the cubic system. It is attracted by a magnet but does not attract iron itself.
Malmesbury group
An 830 to 980 million-year-old basal group of the Western Cape comprising at least eight distinct formations, including the Tygerberg, Piketberg, Porterville, Berg river, Klipplaat, Moorreesburg, Franschhoek, and Bridgetown formations.
mantle
The highly viscous layer of molten rock situated directly beneath the Earth's crust and above the outer core.
marble
A fine to coarse-grained granoblastic calcium carbonate that effervesces in dilute hydrochloric acid. Often banded with various colours and sometimes veined.
marine terrace
A narrow, flat area often seen at the base of a sea cliff caused by the action of the waves.
marl
A calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite.
massive
A description applied to a homogeneous rock which lacks internal structure or layers.
mélange
Large-scale breccia formed in the accretionary wedge above a subduction zone.
melanocratic
A term applied to rocks which are abnormally rich in dark and heavy ferro-magnesium minerals.
mesocratic
A term applied to igneous rocks which in respect of their content of dark silicates are intermediate between those of leucocratic and melanocratic type, and contain 30–60% of dark heavy minerals.
Mesozoic
The era of geological time including the Triassic, Jurassic, and Cretaceous ages.
metamorphic rock
metamorphism
The solid-state recrystallisation of pre-existing rocks due to changes in heat, pressure, or water-rock interactions, i.e. without melting.
metapelite
A metamorphosed pelite (fine grain, clayey) rock.

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metasilicate
A salt of the non-existing metasilicic acid H2SiO3 based on an analogy with the carbonate system.
metatexis
Low-grade anatexis: partial or differential melting of rock components with a low melting point.
mica
Any of a set of minerals which crystallise in the monoclinic system. They have similar chemical compositions and highly perfect basal cleavage.
micropaleontology
A branch of paleontology which studies microfossils.
mid-oceanic ridge
An underwater mountain range typically having a valley known as a rift running along its axis, formed by plate tectonics.
migmatite
A composite rock composed of igneous or igneous-looking and/or metamorphic materials which are generally distinguishable megascopically.
mineral
mineralization
The hydrothermal deposition of economically important metals in the formation of ore bodies or "lodes".
mineralogy
miogeosyncline
A geosyncline in which volcanism is not associated with sedimentation, or the non-volcanic part of the orthogeosyncline located near the craton.
Mohs scale of mineral hardness
Also simply called the Mohs scale.
molasse
A partly marine, partly continental or deltaic sedimentary facies consisting of a very thick sequence of soft ungraded cross-bedded fossiliferous conglomerates, sandstones, shales, and marls.
molding
The process of manufacturing by shaping pliable raw material using a rigid frame or model called a mold.
montmorillonite
Swelling clay mineral with a three layer 2:1 (TOT) structure whose interlayers are mainly occupied by hydrated Na+ and Ca2+ cations and water molecules. The name comes from Montmorillon, France. Montmorillonite and smectite are two interchangeable synonyms, the first being preferentially used in the US while the second one is more frequent in the literature from UK and Europe. See also bentonite.
monocline
A fold with a single limb which produces a sudden steepening of the dip; the rocks, however, soon approximate to horizontal on either side of this flexure.
monoclinic
Having three crystal axes of unequal lengths, with one intersection oblique and the other two perpendicular.
moraine
A glacially formed accumulation of unconsolidated debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past ice age.
mullion
A particular type of reworked boudin. The term is likely derived from an architectural structure with the same name.
muscovite
The common or white mica; for the most part an orthosilicate of aluminium and potassium that crystallises in the monoclinic system.
== N ==
Namibian age
900 to 542 Ma (Neoproterozoic).
Neogene
A geologic period starting 23 million years ago and, depending on definition, either lasting until today or ending 2.6 million years ago with the beginning of the Quaternary.
nodule
A small, irregularly rounded lump or mass of a mineral or mineral aggregate with a contrasting composition to the enclosing sediment or rock. Not to be confused with concretion.
non-clastic
Having the properties of any chemically and/or organically deposited rock, such as limestones, chalks, and evaporite deposits.
normal fault
Also called an extensional fault.
Dip-slip faults can be sub-classified into the types "reverse" and "normal". A normal fault occurs when the crust is extended such that the hanging wall moves downward relative to the footwall. Contrast reverse fault.
== O ==
obsidian
oligoclase
One of the plagioclase feldspars consisting of the albite and anorthite molecules combined in the proportions 9:1 to 7:3. It is found especially in the more acid igneous rocks.
olivine
An orthosilicate mineral of iron and magnesium which crystallises in the orthorhombic system and occurs widely in the basic and ultramafic igneous rocks. It includes olivine-gabbro, olivine–dolerite, olivine-basalt, and peridotites, among others.
Ordovician
A geologic period and system, the second of six of the Paleozoic Era, spanning the time between 485.4 ± 1.9 to 443.4 ± 1.5 million years ago. It follows the Cambrian and is followed by the Silurian.
orogenesis
The formation and growth of mountains related to tectonic activity.
orogeny
Any set of forces and events leading to a large structural deformation of the Earth's lithosphere due to the engagement of tectonic plates. It is the primary mechanism by which mountains are built on continents.
orthoclase
A silicate of potassium and aluminium which crystallises in the monoclinic system and occurs as an essential constituent in granitic and syenitic rocks and as an accessory in many other rock types.
orthogeosyncline
A geosyncline between continental and oceanic cratons containing both volcanic and non-volcanic belts.
orthorhombic
Having a crystal structure with three perpendicular axes all of different lengths.
orthosilicate
An obsolete classification based on the totally deprotonated tetrahedral SiO4−4 anion of the monomeric orthosilicic acid, H4SiO4, or Si(OH)4. Compare with the hypothetical and non-existing planar trigonal metasilicate SiO2−3 anion imagined from the analogy to the carbonate, CO2−3, anion.
oxbow lake
A crescent-shaped lake found within a floodplain or fluvial terrace created by the cut-off and abandonment of an active meander within a river or stream channel.
== P ==
pahoehoe
A type of vesicular, basaltic lava often with a ropy surface texture.
Palaeozoic
Also spelled Paleozoic.
The earliest of the three geologic eras of the Phanerozoic Eon, spanning the time from roughly 541 to 252.2 million years ago. It is the longest of the Phanerozoic eras and is subdivided into six geologic periods: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic Era follows the Neoproterozoic Era of the Proterozoic Eon, and is followed by the Mesozoic Era.
paleocurrent
An indication of the direction of fluid flow (at the time of deposition) visible in a rock.
paleontology
The scientific study of the biological life of the past, primarily through the study of fossils.
palagonite
An alteration product from the interaction of water with volcanic glass of chemical composition similar to basalt or from the interaction between water and basalt melt.
paralithic
A weathered layer of bedrock.
pegmatite
An exceptionally coarse-grained igneous rock.
pelite
A descriptive name for a clastic rock with a grain size of less than 1/16 mm (originally sand or silt).
peridotite
An olive green when fresh, medium brown when weathered, saccharoidal intrusive igneous rock composed mainly of olivine, sometimes with pyroxene.
petrology
The branch of geology that studies the origin, composition, distribution, and structure of rocks.

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phenoclast
A large, conspicuous fragment in sediment or sedimentary rock composed of various sizes of material.
phenocryst
A relatively large crystal in an igneous rock.
phyllite
Any of a set of argillaceous rocks in a condition of metamorphism between slate and mica-schist.
phyllonite
A rock that macroscopically resembles phyllite but that is formed by mechanical degradation (mylonization) of initially coarser rocks (e.g., graywacke, granite, or gneiss).
piercing point
A feature that is cut by a fault and moved. Reconstruction of that object can show how much the fault has moved.
pillar
A vertical, standing, often spire-shaped, natural rock formation.
pitchstone
A black, opaque volcanic glass that may contain irregular, whitish clusters of minerals. Resembles pitch in appearance.
plate tectonics
The set of natural processes and phenomena which result in large-scale movements of portions of the Earth's lithosphere, which is fragmented into multiple tectonic plates of various sizes.
Pleistocene
The geologic epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's recent period of repeated glaciations. The Pleistocene is the first epoch of the Quaternary Period and the sixth epoch of the Cenozoic Era.
Pliocene
The geologic period that extends from 5.332 million to 2.588[2] million years Before Present. It is the second-youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene and is followed by the Pleistocene.
pluton
plutonic
Having crystallised at depth within the Earth's crust, used of a rock. Plutonic rocks are slow-cooling and coarse-grained and have relatively low temperatures of final consolidation.
plumose structure
A ladder or grid pattern that occurs during jointing that resembles plumes, oriented perpendicular to the stress, hence which usually form parallel to the upper and lower surfaces of the constituent rock unit.
pneumatolysis
The destructive after-action of the concentrated volatile constituents of a magma, effected after the consolidation of the main body of the magma.
polymictic
polysynthetic twinning
pore water
Water present in rock and soil pore spaces. Also called interstitial water.
porphyroblast
A large mineral crystal in a metamorphic rock which has grown within the finer-grained groundmass.
porphyry
1. A rock that is porphyritic, containing large and small crystals.
2. In mining, a specific deposit containing widely disseminated metals, typically copper.
Precambrian
A non-standard geologic time period immediately preceding the Phanerozoic Eon, divided into several eons of the geologic time scale. It spans from the formation of Earth about 4540 Ma (million years ago) to the beginning of the Cambrian Period, about 541.0 ± 1.0 Ma, when macroscopic hard-shelled animals first appeared in abundance.
precipitate
A rock or mineral precipitated into solid form from an aqueous solution.
pressure solution
Rock deformation mechanism involving minerals dissolution under mechanical stress.
prograde metamorphism
Mineral changes in rocks under increasing pressure and/or temperature conditions.
protolith
The source rock from which a metamorphic, or in some rare cases a sedimentary, rock was formed. In most cases the appropriate sedimentary term is "provenance" rather than "protolith", since the material has been transported.
psammite
A general term for a sandstone, most often used to describe a metamorphosed rock unit with a dominantly sandstone protolith.
pseudomatrix
A weaker material (mainly lithic fragments) that becomes crushed and matrix-like in a rock.
pumice
A light-coloured, highly vesicular volcanic rock of very low density.
pyroclastic flow
A fast-moving current of hot gas and rock (collectively known as tephra), which normally hugs the ground and travels downhill or spreads laterally under gravity.
pyroclastic
A volcanic fragment, such as a volcanic bomb, breadcrust bomb, or achnelith.
pyroxene
Any of a set of mineral species which, although falling into different systems (orthorhombic, monoclinic, and triclinic), are closely related in form and structure. They are metasilicates of calcium, magnesium, and iron with manganese, and less often with sodium, potassium, zirconium, and fluorine.
pyroxenite
A coarse-grained, holocrystalline igneous rock consisting mainly of pyroxenes. It may contain biotite, hornblende, or olivine as accessories.
== Q ==
quartz
quartzite
A compact, hard, very fine-grained white to creamy white rock which breaks into sharp angular fragments. Quartzite is always associated with other metamorphic rocks, while cemented sandstone is always associated with other sedimentary rocks.
Quaternary
The most recent of the three periods of the Cenozoic Era in the standard geologic time scale. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present.
== R ==
reef knoll
Landform comprising an immense pile of calcareous material previously accumulated on an ancient sea floor. Reef knolls can be divided into bioherms and biostromes. A bioherm is a landform of organic sedimentary rock enclosed or surrounded by rock of different origins. A biostrome is a distinctly bedded or broadly lenticular sedimentary rock landform.
regional metamorphism
Over wide areas resulting from deep burial with consequent rise in temperature and static pressure, usually with the help of folding movements that accompany the formation of mountain ranges.
reticulite
A basaltic pumice in which the walls of the vesicles have collapsed, leaving a network of fine, interconnecting glass threads. It is the lightest rock known.
retrograde metamorphism
The reconstitution of a rock via revolatisation under decreasing temperatures (and usually pressures), allowing the mineral assemblages formed in prograde metamorphism to revert to those more stable at less extreme conditions.
reverse fault
Also called a thrust fault.
Dip-slip faults can be sub-classified into the types "reverse" and "normal". A reverse fault occurs when the crust is compressed such that the hanging wall moves upward relative to the footwall. Contrast normal fault.
rhyolite
An aphanitic, buff to greyish flow-banded rock, often containing spherulites or phenocrysts of quartz and feldspar.
rift
roche moutonnée
An elongated post-glacial rock formation with a smoothed surface on the uphill side and a "plucked" surface on the downhill side.
rock
rolling hills
undulating low hill terrain; cf. "Hügelland"
rudaceous
Having the composition and characteristics of clastic rocks, i.e. coarse-grained sedimentary rocks, conglomerates, and breccias, with a particle size of less than 2 mm.

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rudite
A generic term for any of a set of sedimentary rocks composed of rounded or angular detrital grains, i.e. granules, pebbles, cobbles, and boulders, which are coarser than sand in size.
== S ==
saccharoidal
Having a texture similar to that of granulated sugar.
Saldanian orogeny
sand
sandstone
Sand (with grains up to 2 mm in diameter) in which the grains are cemented together by secondary silica or calcite. Sandstone may be loosely cemented and soft or well cemented and hard, and is usually buff to brownish in color, sometimes reddish, due to the presence of iron oxides, or greenish, due to the presence of glauconite.
sanidine
A form of potash feldspar identical in composition with orthoclase but physically different, formed under different conditions and occurring in different rock types. It is the high temperature form of orthoclase, into which it inverts at 900 °C (1,650 °F). Occurs in lavas and dyke rocks.
schist
A group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. In French, schist is understood as shale.
scree
See talus.
sediment trap
A depression in which sediments substantially accumulate over time.
sedimentary rock
sequence
A sequence of geological events, processes, or rocks arranged in chronological order.
sericite
A white potash-mica, similar to muscovite in chemical composition and general character but occurring as a secondary mineral, often as a decomposition product of orthoclase.
shale
A fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite.
shear zone
A tabular to sheet-like, planar or curviplanar zone composed of rocks that are more highly strained than rocks adjacent to the zone. See also fault.
shield
A large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas.
shingle beach
A beach which is armoured with pebbles or small- to medium-sized cobbles (as opposed to fine sand), typically ranging from 2 to 200 millimetres (0.1 to 7.9 in) diameter.
silcrete
An indurated soil duricrust formed when surface sand and gravel are cemented by dissolved silica.
silt
Granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment (also known as suspended load) in a surface water body. It may also exist as soil deposited at the bottom of a water body.
siltstone
Indurated silt whose granulometry is somewhere between that of sand and clay.
slate
Very fine-grained sedimentary rock of the clay or silt grade which as a consequence of regional metamorphism has developed a slaty cleavage.
slaty cleavage
The property of splitting easily along regular, closely spaced planes of fissility, produced by pressure in fine-grained rocks, with the cleavage planes lying in the directions of maximum elongation of the mass.
slickenside
A smoothly polished surface caused by frictional movement between rocks along the two sides of a fault. This surface is normally striated in the direction of movement.
slump
A form of mass wasting that occurs when a coherent mass of loosely consolidated materials or rock layers moves a short distance down a slope.
snowball Earth
Series of global glaciations in the Precambrian, 600 to 700 million years ago, before the hard-shelled animal life explosion.
smectite
Swelling clay minerals with a three-layer 2:1 (TOT) structure whose interlayers are mainly occupied by Na+ or Ca2+ hydrated cations and water molecules (from Ancient Greek σμηκτός (smēktós) 'lubricated'; from σμηκτρίς (smēktrís) 'walker's earth, fuller's earth'; lit. 'rubbing earth; earth that has the property of cleaning'). See also montmorillonite and bentonite. For non-swelling 2:1 clay minerals, see illite and chlorite.
soil liquefaction
The process describing the behavior of soils that, when loaded, suddenly suffer a transition from a solid state to a liquefied state, or which have the consistency of a heavy liquid.
sorting
Sorting describes the distribution of grain size of sediments, either in unconsolidated deposits or in sedimentary rocks. Very poorly sorted indicates that the sediment sizes are mixed (large variance); whereas well sorted indicates that the sediment sizes are similar (low variance).
speleothem
A geological formation by mineral deposits that accumulate over time in natural caves. Speleothems most commonly form in calcareous caves due to carbonate dissolution reactions. They can take a variety of forms, depending on their depositional history and environment. Their chemical composition, gradual growth, and preservation in caves make them useful paleoclimatic proxies. Includes stalactites and stalagmites.
sphene
Ancient deprecated name for a calcium titanium nesosilicate mineral, CaTiSiO5.
Since 1982, officially called titanite by the International Mineralogical Association.
staurolite
A red brown to black, mostly opaque, nesosilicate mineral with a white streak.
stone
storm ridge
A beach ridge usually located further or higher inland caused by wave action from storms.
strain
A change in the volume or shape of a rock mass in response to stress.
stratigraphy
stratum
stylolite
An irregular discontinuity or non-structural fracture in limestone and other sedimentary rocks. Stylolites result from compaction and pressure solution during diagenesis.
surficial
Of or pertaining to the surface.
syenite
A coarse-grained igneous rock of intermediate composition, composed essentially of alkali-feldspar to the extent of at least two thirds of the total, with a variable content of mafic materials, of which common hornblende is characteristic.
syncline
A geological fold with strata dipping inwards towards the fold axis. Contrast anticline.
syntaxis
An abrupt change in the orientation of a mountain belt or individual fold/thrust structure
== T ==
Table Mountain Group
A group of rock formations within the Cape Supergroup sequence of rocks.
talus
Also called scree.
A collection of broken rock fragments at the base of crags, mountain cliffs, volcanoes or valley shoulders that has accumulated through periodic rockfall from adjacent cliff faces. Landforms associated with these materials are often called talus deposits.
tectonic plate
tekton
tektite
Natural glass formed from terrestrial ejecta during a meteorite impact.

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tempestite
Storm deposits found in sedimentary formations where shell debris accumulate under the effect of waves and seawater movement.
tenacity
A mineral's behavior when deformed or broken.
tephra
Fragmental material produced by a volcanic eruption regardless of composition, fragment size or emplacement mechanism. Once clasts have fallen to the ground they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff.
Tethys Ocean
A prehistoric ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.
till
Also called glacial till.
Unsorted glacial sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier.
tillite
A type of sedimentary rock derived from glacial till which has been indurated or lithified by subsequent burial into solid rock.
titanite
A calcium titanium nesosilicate mineral, CaTiSiO5. See also sphene.
topography
The arrangement of the natural and artificial physical features of an area.
tor
A large, free-standing residual mass (rock outcrop) that rises abruptly from the surrounding smooth and gentle slopes of a rounded hill summit or ridge crest.
trace fossil
trachyte
A fine-grained igneous rock type of intermediate composition, in most cases with little or no quartz, consisting largely of alkali-feldspars (sanidene or oligooclase) together with a small amount of coloured silicates such as diopside, horneblende, or mica.
travertine
A terrestrial sedimentary rock formed by the precipitation of carbonate minerals from solution in ground and surface waters and/or geothermally heated hot springs.
triclinic
In the triclinic system, the crystal is described by vectors of unequal length, and none of the three vectors are orthogonal to another.
tuff
A rock formed of compacted volcanic fragments, some of which can be distinguished by the naked eye. If the fragments are larger than the rock grades into an agglomerate.
tundra
A vast, flat, treeless Arctic region of Europe, Asia, and North America in which the subsoil is permanently frozen.
turbidite
The deposit of a turbidity current.
turbidity current
A current of rapidly moving, sediment-laden water moving down a slope through water, or another fluid. The current moves because it has a higher density than the fluid through which it flows.
Tygerberg formation
A component of the PreCambrian Malmesbury group of South Africa
== U ==
ultramafic
Sometimes used interchangeably with ultrabasic.
Almost feldspar-free. Examples of ultramafic rocks include dunite, peridotite, and pyroxenite.
undulating hills
see "rolling hills"
Urgonian
A shallow-water carbonate facies deposited along the northern margins of the Tethys Ocean during the Barremian and Aptian.
== V ==
vacuole
A bubble inclusion within mineral grains (typically monocrystalline quartz), filled with liquid, gas, or both liquid and gas. Vacuoles are randomly distributed in contrast to the oriented bubble trains of Boehm Lamellae.
Variscan orogeny
Also called the Hercynian orogeny.
A geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea.
varve
An annual layer of sediment or sedimentary rock.
vein
A mineral filling of a fracture or other crack within a rock in a sheet-like or tabular shape.
vermiculite
A hydrous silicate mineral that is classified as a phyllosilicate and that expands greatly when heated. Exfoliation occurs when the mineral is heated sufficiently.
vergence
The direction of overturning of asymmetric folds, which matches the direction of thrusting.
vesiculated
vitrinite
A group of macerals that are the most common component of coal.
vitrophyre
See pitchstone.
volcanic
Rocks that have crystallised from magma poured out at the surface or introduced at shallow depth. They have cooled relatively rapidly, the grain size of the crystals is small, some part of the melt may solidify as glass, volatiles are lost and anhydrous minerals with high temperatures of crystallisation are present.
volcanic bomb
Rounded or spindle-shaped rock of mainly basaltic composition ejected during eruptions.
vug
A small cavity in a rock filled or lined with crystals or minerals that are different from the host rock.
== W ==
wiggle trace
A graph that plots wave amplitudes (recorded by seismic reflection and borehole logging) as a function of time, with the positive peaks shaded in a single dark colour.
wolframite
An iron manganese tungstate mineral with the chemical formula (Fe,Mn)WO4.
== X ==
xenolith
A rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. In geology, the term is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption.
xenotime
A rare earth phosphate mineral whose major component is yttrium orthophosphate (YPO4).
X-ray diffraction (XRD)
A method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and diffracts into many specific directions.
X-ray fluorescence (XRF)
The emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis and chemical analysis of minerals.
xyloid coal
Also called lignite or brown coal.
A soft brown fuel with characteristics that put it somewhere between coal and peat.
== Y ==
Yellowcake
Also urania.
A kind of uranium concentrate powder obtained from leach solutions in an intermediate step in the enrichment of uranium ores.
Young's modulus
Also called the tensile modulus.
In solid mechanics, a measure of the stiffness of an isotropic elastic material. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's law holds.
Ypresian
The oldest age or the lowest stratigraphic stage of the Eocene. It spans the time between ~56 Ma and ~49 Ma (million years ago).
== Z ==
zeolite
Microporous, aluminosilicate minerals commonly used as adsorbents.
zircon
A zirconium silicate mineral belonging to the group of nesosilicates. Its corresponding chemical formula is ZrSiO4.
== See also ==
Outline of geology
Index of geology articles
Glossary of geography terms
Glossary of landforms
== References ==
== External links ==
Schlumberger (2022). "Schlumberger | Energy Glossary". glossary.slb.com. Retrieved 25 October 2022.

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The language of mathematics has a wide vocabulary of specialist and technical terms. It also has a certain amount of jargon: commonly used phrases which are part of the culture of mathematics, rather than of the subject. Jargon often appears in lectures, and sometimes in print, as informal shorthand for rigorous arguments or precise ideas. Much of this uses common English words, but with a specific non-obvious meaning when used in a mathematical sense.
Some phrases, like "in general", appear below in more than one section.
== Philosophy of mathematics ==
abstract nonsense
A tongue-in-cheek reference to category theory, using which one can employ arguments that establish a (possibly concrete) result without reference to any specifics of the present problem. For that reason, it is also known as general abstract nonsense or generalized abstract nonsense.
[The paper of Eilenberg and Mac Lane (1942)] introduced the very abstract idea of a 'category' — a subject then called 'general abstract nonsense'!
[Grothendieck] raised algebraic geometry to a new level of abstraction...if certain mathematicians could console themselves for a time with the hope that all these complicated structures were 'abstract nonsense'...the later papers of Grothendieck and others showed that classical problems...which had resisted efforts of several generations of talented mathematicians, could be solved in terms of...complicated concepts.
canonical
A reference to a standard or choice-free presentation of some mathematical object (e.g., canonical map, canonical form, or canonical ordering). The same term can also be used more informally to refer to something "standard" or "classic". For example, one might say that Euclid's proof is the "canonical proof" of the infinitude of primes.
There are two canonical proofs that are always used to show non-mathematicians what a mathematical proof is like:
deep
A result is called "deep" if its proof requires concepts and methods that are advanced beyond the concepts needed to formulate the result. For example, the prime number theorem – originally proved using techniques of complex analysis – was once thought to be a deep result until elementary proofs were found. On the other hand, the fact that π is irrational is usually known to be a deep result, because it requires a considerable development of real analysis before the proof can be established – even though the claim itself can be stated in terms of simple number theory and geometry.
elegant
An aesthetic term referring to the ability of an idea to provide insight into mathematics, whether by unifying disparate fields, introducing a new perspective on a single field, or by providing a technique of proof which is either particularly simple, or which captures the intuition or imagination as to why the result it proves is true. In some occasions, the term "beautiful" can also be used to the same effect, though Gian-Carlo Rota distinguished between elegance of presentation and beauty of concept, saying that for example, some topics could be written about elegantly although the mathematical content is not beautiful, and some theorems or proofs are beautiful but may be written about inelegantly.
The beauty of a mathematical theory is independent of the aesthetic qualities...of the theory's rigorous expositions. Some beautiful theories may never be given a presentation which matches their beauty....Instances can also be found of mediocre theories of questionable beauty which are given brilliant, exciting expositions....[Category theory] is rich in beautiful and insightful definitions and poor in elegant proofs....[The theorems] remain clumsy and dull....[Expositions of projective geometry] vied for one another in elegance of presentation and in cleverness of proof....In retrospect, one wonders what all the fuss was about.Mathematicians may say that a theorem is beautiful when they really mean to say that it is enlightening. We acknowledge a theorem's beauty when we see how the theorem 'fits' in its place....We say that a proof is beautiful when such a proof finally gives away the secret of the theorem....
elementary
A proof or a result is called "elementary" if it only involves basic concepts and methods in the field, and is to be contrasted with deep results which require more development within or outside the field. The concept of "elementary proof" is used specifically in number theory, where it usually refers to a proof that does not resort to methods from complex analysis.
folklore
A result is called "folklore" if it is non-obvious and non-published, yet generally known to the specialists within a field. In many scenarios, it is unclear as to who first obtained the result, though if the result is significant, it may eventually find its way into the textbooks, whereupon it ceases to be folklore.
Many of the results mentioned in this paper should be considered "folklore" in that they merely formally state ideas that are well-known to researchers in the area, but may not be obvious to beginners and to the best of my knowledge do not appear elsewhere in print.
natural
Similar to "canonical" but more specific, and which makes reference to a description (almost exclusively in the context of transformations) which holds independently of any choices. Though long used informally, this term has found a formal definition in category theory.
pathological
An object behaves pathologically (or, somewhat more broadly used, in a degenerated way) if it either fails to conform to the generic behavior of such objects, fails to satisfy certain context-dependent regularity properties, or simply disobeys mathematical intuition. In many occasions, these can be and often are contradictory requirements, while in other occasions, the term is more deliberately used to refer to an object artificially constructed as a counterexample to these properties. A simple example is that from the definition of a triangle having angles which sum to π radians, a single straight line conforms to this definition pathologically.
Since half a century we have seen arise a crowd of bizarre functions which seem to try to resemble as little as possible the honest functions which serve some purpose....Nay more, from the logical point of view, it is these strange functions which are the most general....to-day they are invented expressly to put at fault the reasonings of our fathers....
[The Dirichlet function] took on an enormous importance...as giving an incentive for the creation of new types of function whose properties departed completely from what intuitively seemed admissible. A celebrated example of such a so-called 'pathological' function...is the one provided by Weierstrass....This function is continuous but not differentiable.
Note for that latter quote that as the differentiable functions are meagre in the space of continuous functions, as Banach found out in 1931, differentiable functions are colloquially speaking a rare exception among the continuous ones. Thus it can hardly be defended any-more to call non-differentiable continuous functions pathological.
rigor (rigour)
The act of establishing a mathematical result using indisputable logic, rather than informal descriptive argument. Rigor is a cornerstone quality of mathematics, and can play an important role in preventing mathematics from degenerating into fallacies.
well-behaved
An object is well-behaved (in contrast with being Pathological) if it satisfies certain prevailing regularity properties, or if it conforms to mathematical intuition (even though intuition can often suggest opposite behaviors as well). In some occasions (e.g., analysis), the term "smooth" can also be used to the same effect.

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== Descriptive informalities ==
Although ultimately every mathematical argument must meet a high standard of precision, mathematicians use descriptive but informal statements to discuss recurring themes or concepts with unwieldy formal statements. Note that many of the terms are completely rigorous in context.

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almost all
A shorthand term for "all except for a set of measure zero", when there is a measure to speak of, with the phrases almost surely and almost everywhere having related meanings. For example, "almost all real numbers are transcendental" because the algebraic real numbers form a countable subset of the real numbers with measure zero. One can also speak of "almost all" integers having a property to mean "all except finitely many", despite the integers not admitting a measure for which this agrees with the previous usage, such as "almost all prime numbers are odd". There is a more complicated meaning for integers as well, discussed in the main article. Finally, this term is sometimes used synonymously with generic, below. arbitrarily large
Notions which arise mostly in the context of limits, referring to the recurrence of a phenomenon as the limit is approached. A statement such as that predicate P is satisfied by arbitrarily large values, can be expressed in more formal notation by ∀x : ∃y ≥ x : P(y). See also frequently. The statement that quantity f(x) depending on x "can be made" arbitrarily large, corresponds to ∀y : ∃x : f(x) ≥ y. arbitrary
A shorthand for the universal quantifier. An arbitrary choice is one which is made unrestrictedly, or alternatively, a statement holds of an arbitrary element of a set if it holds of any element of that set. Also much in general-language use among mathematicians: "Of course, this problem can be arbitrarily complicated". eventually
In the context of limits, this is shorthand meaning for sufficiently large arguments; the relevant argument(s) are implicit in the context. As an example, the function log(log(x)) eventually becomes larger than 100"; in this context, "eventually" means "for sufficiently large x."
factor through
A term in category theory referring to composition of morphisms. If for three objects A, B, and C a map
f
:
A
→
C
{\displaystyle f\colon A\to C}
can be written as a composition
f
=
h
∘
g
{\displaystyle f=h\circ g}
with
g
:
A
→
B
{\displaystyle g\colon A\to B}
and
h
:
B
→
C
{\displaystyle h\colon B\to C}
, then f is said to factor through any (and all) of
B
{\displaystyle B}
,
g
{\displaystyle g}
, and
h
{\displaystyle h}
. finite
When said of the value of a variable assuming values from the non-negative extended reals
R
≥
0
∪
{
∞
}
,
{\displaystyle \mathbb {R} _{\geq 0}\cup \{\infty \},}
the meaning is usually "not infinite". For example, if the variance of a random variable is said to be finite, this implies it is a non-negative real number, possibly zero. In some contexts though, for example in "a small but finite amplitude", zero and infinitesimals are meant to be excluded. When said of the value of a variable assuming values from the extended natural numbers
N
∪
{
∞
}
,
{\displaystyle \mathbb {N} \cup \{\infty \},}
the meaning is simply "not infinite". When said of a set or a mathematical object whose main component is a set, it means that the cardinality of the set is less than
ℵ
0
{\displaystyle \aleph _{0}}
. frequently
In the context of limits, this is shorthand for arbitrarily large arguments and its relatives; as with eventually, the intended variant is implicit. As an example, the sequence
(
−
1
)
n
{\displaystyle (-1)^{n}}
is frequently in the interval (1/2, 3/2), because there are arbitrarily large n for which the value of the sequence is in the interval. formal, formally
Qualifies anything that is sufficiently precise to be translated straightforwardly in a formal system. For example. a formal proof, a formal definition. generic
This term has similar connotations as almost all but is used particularly for concepts outside the purview of measure theory. A property holds "generically" on a set if the set satisfies some (context-dependent) notion of density, or perhaps if its complement satisfies some (context-dependent) notion of smallness. For example, a property which holds on a dense Gδ (intersection of countably many open sets) is said to hold generically. In algebraic geometry, one says that a property of points on an algebraic variety that holds on a dense Zariski open set is true generically; however, it is usually not said that a property which holds merely on a dense set (which is not Zariski open) is generic in this situation. in general
In a descriptive context, this phrase introduces a simple characterization of a broad class of objects, with an eye towards identifying a unifying principle. This term introduces an "elegant" description which holds for "arbitrary" objects. Exceptions to this description may be mentioned explicitly, as "pathological" cases. Norbert A'Campo of the University of Basel once asked Grothendieck about something related to the Platonic solids. Grothendieck advised caution. The Platonic solids are so beautiful and so exceptional, he said, that one cannot assume such exceptional beauty will hold in more general situations. left-hand side, right-hand side (LHS, RHS)
Most often, these refer simply to the left-hand or the right-hand side of an equation; for example,
x
=
y
+
1
{\displaystyle x=y+1}
has
x
{\displaystyle x}
on the LHS and
y
+
1
{\displaystyle y+1}
on the RHS. Occasionally, these are used in the sense of lvalue and rvalue: an RHS is primitive, and an LHS is derivative. nice
A mathematical object is colloquially called nice or sufficiently nice if it satisfies hypotheses or properties, sometimes unspecified or even unknown, that are especially desirable in a given context. It is an informal antonym for pathological. For example, one might conjecture that a differential operator ought to satisfy a certain boundedness condition "for nice test functions," or one might state that some interesting topological invariant should be computable "for nice spaces X."
object
Anything that can be assigned to a variable and for which equality with another object can be considered. The term was coined when variables began to be used for sets and mathematical structures. onto
A function (which in mathematics is generally defined as mapping the elements of one set A to elements of another B) is called "A onto B" (instead of "A to B" or "A into B") only if it is surjective; it may even be said that "f is onto" (i. e. surjective). Not translatable (without circumlocutions) to some languages other than English. proper
If, for some notion of substructure, objects are substructures of themselves (that is, the relationship is reflexive), then the qualification proper requires the objects to be different. For example, a proper subset of a set S is a subset of S that is different from S, and a proper divisor of a number n is a divisor of n that is different from n. This overloaded word is also non-jargon for a proper morphism. property
A characteristic that a mathematical object may have or not; for example "being positive". Properties are often expressed with formulas and are used for specifying sets and subsets, typically with set-builder notation. regular
A function is called regular if it satisfies satisfactory continuity and differentiability properties, which are often context-dependent.

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These properties might include possessing a specified number of derivatives, with the function and its derivatives exhibiting some nice property (see nice above), such as Hölder continuity. Informally, this term is sometimes used synonymously with smooth, below. These imprecise uses of the word regular are not to be confused with the notion of a regular topological space, which is rigorously defined. resp. (Respectively) A convention to shorten parallel expositions. "A (resp. B) [has some relationship to] X (resp. Y)" means that A [has some relationship to] X and also that B [has (the same) relationship to] Y. For example, squares (resp. triangles) have 4 sides (resp. 3 sides); or compact (resp. Lindelöf) spaces are ones where every open cover has a finite (resp. countable) open subcover. sharp
Often, a mathematical theorem will establish constraints on the behavior of some object; for example, a function will be shown to have an upper or lower bound. The constraint is sharp (sometimes optimal) if it cannot be made more restrictive without failing in some cases. For example, for arbitrary non-negative real numbers x, the exponential function ex, where e = 2.7182818..., gives an upper bound on the values of the quadratic function x2. This is not sharp; the gap between the functions is everywhere at least 1. Among the exponential functions of the form αx, setting α = e2/e = 2.0870652... results in a sharp upper bound; the slightly smaller choice α = 2 fails to produce an upper bound, since then α3 = 8 < 32. In applied fields the word "tight" is often used with the same meaning. smooth
Smoothness is a concept which mathematics has endowed with many meanings, from simple differentiability to infinite differentiability to analyticity, and still others which are more complicated. Each such usage attempts to invoke the physically intuitive notion of smoothness. strong, stronger
A theorem is said to be strong if it deduces restrictive results from general hypotheses. One celebrated example is Donaldson's theorem, which puts tight restraints on what would otherwise appear to be a large class of manifolds. This (informal) usage reflects the opinion of the mathematical community: not only should such a theorem be strong in the descriptive sense (below) but it should also be definitive in its area. A theorem, result, or condition is further called stronger than another one if a proof of the second can be easily obtained from the first but not conversely. An example is the sequence of theorems: Fermat's little theorem, Euler's theorem, Lagrange's theorem, each of which is stronger than the last; another is that a sharp upper bound (see sharp above) is a stronger result than a non-sharp one. Finally, the adjective strong or the adverb strongly may be added to a mathematical notion to indicate a related stronger notion; for example, a strong antichain is an antichain satisfying certain additional conditions, and likewise a strongly regular graph is a regular graph meeting stronger conditions. When used in this way, the stronger notion (such as "strong antichain") is a technical term with a precisely defined meaning; the nature of the extra conditions cannot be derived from the definition of the weaker notion (such as "antichain"). sufficiently large, suitably small, sufficiently close
In the context of limits, these terms refer to some (unspecified, even unknown) point at which a phenomenon prevails as the limit is approached. A statement such as that predicate P holds for sufficiently large values, can be expressed in more formal notation by ∃x : ∀y ≥ x : P(y). See also eventually. upstairs, downstairs
A descriptive term referring to notation in which two objects are written one above the other; the upper one is upstairs and the lower, downstairs. For example, in a fiber bundle, the total space is often said to be upstairs, with the base space downstairs. In a fraction, the numerator is occasionally referred to as upstairs and the denominator downstairs, as in "bringing a term upstairs". up to, modulo, mod out by
An extension to mathematical discourse of the notions of modular arithmetic. A statement is true up to a condition if the establishment of that condition is the only impediment to the truth of the statement. Also used when working with members of equivalence classes, especially in category theory, where the equivalence relation is (categorical) isomorphism; for example, "The tensor product in a weak monoidal category is associative and unital up to a natural isomorphism."
vanish
To assume the value 0. For example, "The function sin(x) vanishes for those values of x that are integer multiples of π." This can also apply to limits: see Vanish at infinity. weak, weaker
The converse of strong. well-defined
Accurately and precisely described or specified. For example, sometimes a definition relies on a choice of some object; the result of the definition must then be independent of this choice.

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== Proof terminology ==
The formal language of proof draws repeatedly from a small pool of ideas, many of which are invoked through various lexical shorthands in practice.
aliter
An obsolescent term which is used to announce to the reader an alternative method, or proof of a result. In a proof, it therefore flags a piece of reasoning that is superfluous from a logical point of view, but has some other interest.
by way of contradiction (BWOC), or "for, if not, ..."
The rhetorical prelude to a proof by contradiction, preceding the negation of the statement to be proved.
if and only if (iff)
An abbreviation for logical equivalence of statements.
in general
In the context of proofs, this phrase is often seen in induction arguments when passing from the base case to the induction step, and similarly, in the definition of sequences whose first few terms are exhibited as examples of the formula giving every term of the sequence.
necessary and sufficient
A minor variant on "if and only if"; "A is necessary (and sufficient) for B" means "A if (only if) B". For example, "For a field K to be algebraically closed it is necessary and sufficient that it have no finite field extensions" means "K is algebraically closed if and only if it has no finite extensions". Often used in lists, as in "The following conditions are necessary and sufficient for a field to be algebraically closed...".
need to show (NTS), required to prove (RTP), wish to show, want to show (WTS)
Proofs sometimes proceed by enumerating several conditions whose satisfaction will together imply the desired theorem; thus, one needs to show just these statements.
one and only one
A statement of the existence and uniqueness of an object; the object exists, and furthermore, no other such object exists.
Q.E.D.
(Quod erat demonstrandum): A Latin abbreviation, meaning "which was to be demonstrated", historically placed at the end of proofs, but less common currently, having been supplanted by the Halmos end-of-proof mark, a square sign ∎.
sufficiently nice
A condition on objects in the scope of the discussion, to be specified later, that will guarantee that some stated property holds for them. When working out a theorem, the use of this expression in the statement of the theorem indicates that the conditions involved may be not yet known to the speaker, and that the intent is to collect the conditions that will be found to be needed in order for the proof of the theorem to go through.
the following are equivalent (TFAE)
Often several equivalent conditions (especially for a definition, such as normal subgroup) are equally useful in practice; one introduces a theorem stating an equivalence of more than two statements with TFAE.
transport of structure
It is often the case that two objects are shown to be equivalent in some way, and that one of them is endowed with additional structure. Using the equivalence, we may define such a structure on the second object as well, via transport of structure. For example, any two vector spaces of the same dimension are isomorphic; if one of them is given an inner product and if we fix a particular isomorphism, then we may define an inner product on the other space by factoring through the isomorphism.
Let V be a finite-dimensional vector space over k....Let (ei)1≤ i ≤ n be a basis for V....There is an isomorphism of the polynomial algebra k[Tij]1≤ i, j ≤ n onto the algebra Symk(V ⊗ V*)....It extends to an isomorphism of k[GLn] to the localized algebra Symk(V ⊗ V*)D, where D = det(ei ⊗ ej*)....We write k[GL(V)] for this last algebra. By transport of structure, we obtain a linear algebraic group GL(V) isomorphic to GLn.
without (any) loss of generality (WLOG, WOLOG, WALOG), we may assume (WMA)
Sometimes a proposition can be more easily proved with additional assumptions on the objects it concerns. If the proposition as stated follows from this modified one with a simple and minimal explanation (for example, if the remaining special cases are identical but for notation), then the modified assumptions are introduced with this phrase and the altered proposition is proved.
== Proof techniques ==
Mathematicians have several phrases to describe proofs or proof techniques. These are often used as hints for filling in tedious details.

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angle chasing
Used to describe a geometrical proof that involves finding relationships between the various angles in a diagram.
back-of-the-envelope calculation
An informal computation omitting much rigor without sacrificing correctness. Often this computation is "proof of concept" and treats only an accessible special case.
brute force
Rather than finding underlying principles or patterns, this is a method where one would evaluate as many cases as needed to sufficiently prove or provide convincing evidence that the thing in question is true. Sometimes this involves evaluating every possible case (where it is also known as proof by exhaustion).
by example
A proof by example is an argument whereby a statement is not proved but instead illustrated by an example. If done well, the specific example would easily generalize to a general proof.
by inspection
A rhetorical shortcut made by authors who invite the reader to verify, at a glance, the correctness of a proposed expression or deduction. If an expression can be evaluated by straightforward application of simple techniques and without recourse to extended calculation or general theory, then it can be evaluated by inspection. It is also applied to solving equations; for example to find roots of a quadratic equation by inspection is to 'notice' them, or mentally check them. 'By inspection' can play a kind of gestalt role: the answer or solution simply clicks into place.
by intimidation
Style of proof where claims believed by the author to be easily verifiable are labelled as 'obvious' or 'trivial', which often results in the reader being confused.
clearly, can be easily shown
A term which shortcuts around calculation the mathematician perceives to be tedious or routine, accessible to any member of the audience with the necessary expertise in the field; Laplace used obvious (French: évident).
complete intuition
commonly reserved for jokes (puns on complete induction).
diagram chasing
Given a commutative diagram of objects and morphisms between them, if one wishes to prove some property of the morphisms (such as injectivity) which can be stated in terms of elements, then the proof can proceed by tracing the path of elements of various objects around the diagram as successive morphisms are applied to it. That is, one chases elements around the diagram, or does a diagram chase.
handwaving
A non-technique of proof mostly employed in lectures, where formal argument is not strictly necessary. It proceeds by omission of details or even significant ingredients, and is merely a plausibility argument.
in general
In a context not requiring rigor, this phrase often appears as a labor-saving device when the technical details of a complete argument would outweigh the conceptual benefits. The author gives a proof in a simple enough case that the computations are reasonable, and then indicates that "in general" the proof is similar.
index battle
For proofs involving objects with multiple indices which can be solved by going to the bottom (if anyone wishes to take up the effort). Similar to diagram chasing.
morally true
Used to indicate that the speaker believes a statement should be true, given their mathematical experience, even though a proof has not yet been put forward. As a variation, the statement may in fact be false, but instead provide a slogan for or illustration of a correct principle. Hasse's local-global principle is a particularly influential example of this.
obviously
See clearly.
the proof is left as an exercise to the reader
Usually applied to a claim within a larger proof when the proof of that claim can be produced routinely by any member of the audience with the necessary expertise, but is not so simple as to be obvious.
trivial
Similar to clearly. A concept is trivial if it holds by definition, is an immediate corollary to a known statement, or is a simple special case of a more general concept.
== Miscellaneous ==
This section features terms used across different areas in mathematics, or terms that do not typically appear in more specialized glossaries. For the terms used only in some specific areas of mathematics, see glossaries in Category:Glossaries of mathematics.
binary
A binary relation is a set of ordered pairs; an element x is said to be related to another element y if and only if (x,y) are in the set.
correspondence
A correspondence from a set A to a set B is a subset of a Cartesian product A × B ; in other words, it is a binary relation but with the specification of the ambient sets A, B used in the definition.
diagram
A visual representation of the relationship(s) between variables.
function
A function f: A → B is an ordered triple (A, B, f ) consisting of sets A, B and a subset f of the Cartesian product A × B subject to the condition (a, b), (a, b′) ∈ f implies b = b′. In other words, it is a special kind of correspondence where given an element a of A, there is a unique element b of B that corresponds to it.
fundamental
The word fundamental is used to describe a theorem with a given area of mathematics considered to be the most central theorem of that particular area (e.g. Fundamental Theorem of Arithmetic for Arithmetic).
invariant
An invariant of an object or a space is a property or number of the object or a space that remains unchanged under some transformations.
map
A synonym for a function between sets or a morphism in a category. Depending on authors, the term "maps"
or the term "functions" may be reserved for specific kinds of functions or morphisms (e.g., function as an analytic term and map as a general term).
mathematics
See mathematics.

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multivalued
A "multivalued function” from a set A to a set B is a function from A to the subsets of B. It has typically the property that, for almost all points x of B, there is a neighbourhood of x such that the restriction of the function to the neighbourhood can be considered as a set of functions from the neighbourhood to B.
projection
A projection is, roughly, a map from some space or object to another that omits some information on the object or space. For example,
R
2
→
R
,
(
x
,
y
)
↦
x
{\displaystyle \mathbb {R} ^{2}\to \mathbb {R} ,(x,y)\mapsto x}
is a projection and its restriction to a graph of a function, say, is also a projection. The terms “idempotent operator” and “forgetful map” are also synonyms for a projection.
structure
A mathematical structure on an object is an additional set of objects or data attached to the object (e.g., relation, operation, metric, topology).
== See also ==
Glossary of areas of mathematics
List of mathematical constants
List of mathematical symbols
Category:Mathematical terminology
== Notes ==
== References ==
Eilenberg, Samuel; Mac Lane, Saunders (1942), "Natural Isomorphisms in Group Theory", Proc. Natl. Acad. Sci. USA, 28 (12): 537–543, Bibcode:1942PNAS...28..537E, doi:10.1073/pnas.28.12.537, PMC 1078535, PMID 16588584.
Impagliazzo, Russell (1995), "A personal view of average-case complexity", Proc. Tenth Annual Structure in Complexity Theory Conference (SCT'95), pp. 134–147, CiteSeerX 10.1.1.678.8930, doi:10.1109/SCT.1995.514853, ISBN 978-0-8186-7052-7, S2CID 2154064.
Jackson, Allyn (2004), "Comme Appelé du Néant — As If Summoned from the Void: The Life of Alexandre Grothendieck", AMS Notices, 51 (9, 10) (Parts I and II).
Mac Lane, Saunders (1997), "The PNAS way back then" (PDF), Proc. Natl. Acad. Sci. USA, 94 (12): 5983–5985, Bibcode:1997PNAS...94.5983M, doi:10.1073/pnas.94.12.5983, PMC 33670, PMID 9177152.
Mac Lane, Saunders (1998), Categories for the Working Mathematician, Springer.
Monastyrsky, Michael (2001), "Some Trends in Modern Mathematics and the Fields Medal" (PDF), Can. Math. Soc. Notes, 33 (2 and 3).
Pinto, J. Sousa (2004), Hoskins, R.F. (ed.), Infinitesimal methods for mathematical analysis, Horwood Publishing, p. 246, ISBN 978-1-898563-99-0.
Poincare, Henri (1913), Halsted, Bruce (ed.), The Foundations of Science, The Science Press, p. 435.
Rota, Gian-Carlo (1977), "The phenomenology of mathematical beauty", Synthese, 111 (2): 171–182, doi:10.1023/A:1004930722234, ISSN 0039-7857, S2CID 44064821.
Shafarevich, Igor (1991), Kandall, G.A. (ed.), Algebraic Geometry, vol. IV, Springer.
Wiedijk, Freek, ed. (2006), The Seventeen Provers of the World, Birkhäuser, ISBN 978-3-540-30704-4.
== Bibliography ==
Encyclopedia of Mathematics

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This is a glossary of terms used in meteoritics, the science of meteorites.
== # ==
2 Pallas – an asteroid from the asteroid belt and one of the likely parent bodies of the CR meteorites.
4 Vesta – second-largest asteroid in the asteroid belt and likely source of the HED meteorites.
221 Eos – an asteroid from the asteroid belt and one of the likely parent bodies of the CO meteorites.
289 Nenetta – an asteroid from the asteroid belt and one of the likely parent bodies of the angrites.
3103 Eger – an asteroid from the asteroid belt and one of the likely parent bodies of the aubrites.
3819 Robinson – an asteroid from the asteroid belt and one of the likely parent bodies of the angrites.
IA meteorite – an iron meteorite group now part of the IAB group/complex.
IAB meteorite – an iron meteorite and primitive achondrite of the IAB group/complex.
IB meteorite – an iron meteorite group now part of the IAB group/complex.
IC meteorite – an iron meteorite that is part of the IC group.
== A ==
Ablation – the process of a meteorite losing mass during the passage through the atmosphere.
Acapulcoite – a group of primitive achondrites.
Accretion – the process in which matter of the protoplanetary disk coalesces to form planetesimals.
Achondrite – a differentiated meteorite (meaning without chondrules).
Aerolite – an old term for stony meteorites.
ALH – an abbreviation used for meteorites from Allan Hills.
Allan Hills 84001 – is an exotic meteorite from Mars that does not fit into any of the SNC groups and was thought to contain evidence for life on Mars.
Allende meteorite – is the largest carbonaceous chondrite ever found on Earth.
Amphoterite – an obsolete classification of chondritic meteorites that are now classified as LL.
Angrite – a basaltic meteorite.
ANSMET – the Antarctic Search for Meteorites is a scientific program that looks for meteorites in the Transantarctic Mountains.
Asteroidal achondrite – an achondrite that differentiated on an asteroid or planetesimal (see planetary achondrite)
Asteroid spectral types – classification of asteroids according to their spectra.
Ataxite – an iron meteorite that has no visible structures when etched.
Aubrite – a class of achondrite meteorites composed primarily of the orthopyroxene enstatite
== B ==
Basaltic achondrite – a grouping of basalt meteorites (HED meteorites + Angrite)
Brachinite – either a primitive achondrite or an asteroidal achondrite
Bolide – is an extremely bright meteor, especially one that explodes in the atmosphere
== C ==
C – can refer to carbonaceous chondrite or to an iron meteorite designation (Roman numeral and letter).
Carbonaceous chondrite
CAI – an abbreviation of calcium–aluminium-rich inclusion
Calcium–aluminium-rich inclusion
Chassignite
Chondrite – stony meteorites unmodified by melting or differentiation of the parent body
Chondrule – millimetre-scale round grains found in chondrites
Clan – meteorites that are not similar enough to form a group, but are also not too different from each other to be put in separate classes.
Class – two or more groups that have a similar chemistry and oxygen isotope ratios.
Compositional type – a classification based on overall composition, for example stony, iron, stony-iron (as introduced by Maskelyne). Can also refer to the composition deduced from spectroscopy of asteroids.
Condensation – the process of chemicals changing from the gaseous to the solid phase during the cooling of the protoplanetary disk.
Condensation sequence – the sequence of minerals that changes from the gaseous to the solid state while the protoplanetary disk cools.
Cosmic dust – small interplanetary and interstellar particles that are similar to meteorites (See Micrometeorite).
Cosmochemistry – the study of the chemical composition of the universe and its constituents, and the processes that produced those compositions.
== D ==
Dar al Gani – a meteorite field in the Libyan Sahara.
Desert glass – natural glass found in deserts formed from the silica in sand as a result of lightning strikes or meteor impacts.
Differentiated – a meteorite that has undergone igneous differentiation. (See: achondrite)
Differentiation – usually the process of a planetesimal forming an iron core and silicate mantle.
Duo – a grouping of two meteorites that share similar characteristics (see Grouplet).
== E ==
E – can refer to enstatite chondrite or to an iron meteorite designation (Roman numeral and letter).
Eagle Station grouplet – a set of pallasite meteorite specimen that do not fit into any of the defined pallasite groups.
Electrophonic bolide – a meteoroid which produces a measurable discharge of electromagnetic energy (EMP) during its passage through the atmosphere.
Enstatite achondrite – a meteorite that is mostly composed of enstatite. Usually part of the aubrite group.
Enstatite chondrite – a rare form of meteorite thought to comprise only 2% of chondrites.
== F ==
Fall – a meteorite that was seen while it fell to Earth and found.
Find – a meteorite that was found without seeing it fall.
Fossil meteorite – a meteorite that was buried under layers of sediment before the start of the Quaternary period. Some or all of the original cosmic material has been replaced by diagenetic minerals. (It is, however, not a fossil).
Fusion crust – a coating on meteorites that forms during their passage through the atmosphere.
== G ==
Group – a collection of five or more meteorites sharing similar characteristics.
Grouplet – a collection of fewer than five meteorites sharing similar characteristics.
== H ==
Hammer Stone – a specific individual meteorite that has hit either a human, man-made object, and/or an animal.
HED – abbreviation for three basaltic achondrite groups howardite, eucrite and diogenite.
HED meteorite – a clan of basaltic achondrites.
Hexahedrite – a structural class of iron meteorites having a relatively low nickel content
Hunter – a person who searches for meteorites.

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== I ==
Impact breccia – rock composed of fragments of terrestrial, extraterrestrial or mixed origin fused by the energy of impact
Impactite – informal term for a terrestrial rock resulting from the shocking impact of a meteor.
Insoluble organic matter – Kerogen-like macromolecule residue from carbonaceous chondrite meteorites after soluble organic matter has been removed.
Iron–nickel alloy – an alternative expression for meteoric iron.
Iron meteorite – a meteorite that is mainly composed of meteoric iron.
== K ==
Kakangari chondrite – a group of chondrite meteorites.
Kamacite – a native metal (mineral) found in meteorites.
== L ==
Lodranite – member of a small group of primitive achondrites thought to derive from deeper within the same parent body as acapulcoites
Lunaite – a meteorite that originated from the Moon (synonym of Lunar meteorite). Compare Category:Meteorites found on bodies other than Earth.
Lunar meteorite – a meteorite that originated from the Moon (synonym of Lunaite). Compare Category:Meteorites found on bodies other than Earth.
== M ==
Main group pallasite – a pallasite belonging to the main group.
Main mass – the largest/heaviest piece of a fragmented meteorite, typically found in a strewn field.
Magmatic meteorite
Martian meteorite – a meteorite that originated from Mars. Compare Category:Meteorites found on bodies other than Earth.
Maskelynite – a natural glass found in meteorites.
Matrix – the mineral assemblage surrounding chondrules.
Mesosiderite – a grouping of stony-iron meteorite that are breccias.
Meteoric iron – a native metal found in meteorites and a mixture of different mineral phases. Compare telluric iron.
Meteorite Observation and Recovery Program – a scientific program that was centered in Canada.
Meteoriticist – a scientist working on meteorites, meteors, and meteoroids.
Meteoritics – the science of meteorites, meteors, and meteoroids.
MORP – abbreviation for Meteorite Observation and Recovery Program.
Micrometeorite – microscopic meteorites derived from Cosmic dust.
== N ==
Nakhlite – a group of Martian meteorites
Neumann lines (or Neumann bands) – a pattern of fine parallel lines seen in some iron meteorites, thought to be due to impact events on the parent body
Nonmagmatic meteorite – (deprecated) iron meteorites that were thought to have not formed by igneous processes.
== O ==
O – usually refers to ordinary chondrite
Observed fall – a meteorite that was seen when it fell to Earth.
Octahedrite – the most common structural class of iron meteorites.
Ordinary chondrite – a chondrite meteorite, where 'ordinary' means that it is the most common found
== P ==
PAC – abbreviation for primitive achondrite.
Pallasite – a class of stony–iron meteorite.
Panspermia – the hypothesis that life could reach other planets by the means of meteorites and/or comets.
Parent body – the celestial body from which originates a meteorite or a class of meteorites.
Petrologic type – a classification scheme that expresses the degree to which a meteorite has been affected by the secondary processes of thermal metamorphism and aqueous alteration on the parent asteroid.
Pitts grouplet – a grouplet of meteorites that is part of the IAB meteorites.
Planetary achondrite – an achondrite that was differentiated on a planet and not a planetesimal or asteroid (See asteroidal achondrite).
Plessite – a fine grained intergrowth found in meteoric iron consisting of kamacite, taenite and tetrataenite lamella.
Presolar grains – interstellar solid matter in the form of tiny solid grains from a time before the Sun was formed.
Primitive meteorite
Primitive achondrite – a meteorite that has similarities to achondrites and chondrites.
Protoplanetary disk – a circumstellar disk from which all solids in the Solar System formed.
Pyroxene pallasite grouplet
== R ==
Regmaglypts – thumbprint-sized indentations in the surface of larger meteorites formed by ablation as the meteorite passes through a planet's atmosphere, probably caused by vortices of hot gas.
Rose-Tschermak-Brezina classification – a classification developed by Gustav Rose, Gustav Tschermak and Aristides Brezina.
Rumuruti chondrite – a group of chondrites.
== S ==
Shergottite – igneous rocks of mafic to ultramafic lithology, named after a meteorite that fell at Sherghati, India in 1865.
Shock stage – a measure of the degree of fracturing of the matrix of a common chondrite meteorite.
Shock metamorphism – the effects of shock-wave related deformation and heating during impact events.
Siderite – the old term for iron meteorite.
Siderolite – the old term for stony-iron meteorites.
SNC – abbreviation for shergottite, nakhlite and chassignite, the three main types of Martian meteorite.
Solar nebula – a synonym of the protoplanetary disk.
Soluble organic matter – compounds that can be extracted from carbonaceous chondrites using water or other solvents. These compounds include amino acids, carboxylic acids, and nucleotide bases.
Spectral class –
Stony meteorite – a meteorite composed mostly of silicates.
Stony-iron meteorite – a meteorite that is a mixture of meteoric iron and silicates.
Strewn field – a field of fragments from one meteorite fall.
Structural class – a subdivision of iron meteorites in ataxites, hexahedrites and octahedrites.
Superbolide – is a bolide that reaches an apparent magnitude of −17 or brighter, which is roughly 100 times brighter than the full moon. Recent examples of superbolides include the Sutter's Mill meteorite and the Chelyabinsk meteor.
== T ==
Taenite – a native metal (mineral) found in meteorites.
Tamdakht – a meteorite that fell near Ouarzazate, Morocco on 2008-12-20 producing a strewn field of approximately 25 km (16 mi) by 2 km (1.2 mi) and two small impact craters.
Tektite – glassy terrestrial debris created by meteorite impacts.
Thumbprinting – see regmaglypts
Total known weight (TKW) – total known mass of a meteorite.
Trio – a grouping of three meteorites that share similar characteristics (see Grouplet).
Type – subdivision of meteorites. Loosely defined. Usually refers to chondrite, achondrite and sometimes primitive achondrite.
== U ==
Udei Station grouplet – a grouplet of meteorites that is part of the IAB meteorites.
Ungrouped – a meteorite that has not been assigned to a group or grouplet.
Undifferentiated
Ureilite
== V ==
Vesta – second largest asteroid in the asteroid belt and likely source of the HED meteorites.
Volatile elements – are chemical elements that have low boiling and condensation temperatures.
== W ==
Widmanstätten pattern – a fine interleaving of kamacite and taenite bands/ribbons found in octahedrite irons and some pallasites.
Willamette meteorite – the largest meteorite discovered in North America, found in the Willamette Valley of Oregon.
Winonaite – a type of primitive achondrite meteorite.
Weston meteorite – a meteorite which fell to earth above the town of Weston, Connecticut on December 14, 1807.
== References ==

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A graviquake is an earthquake occurring in an extensional tectonic setting, where the gravitational energy stored during the interseismic period is delivered by the collapse of a brittle upper crustal volume, slipping along a normal fault and generating the double couple recorded in the moment tensor solution.
== References ==

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The head of the valley or, less commonly, the valley head, refers to the uppermost part of a valley.
== Description ==
The head of a valley may take widely differing forms; for example, in highland regions the valley often ends in a broad, evenly sloping hollow. The higher the head of the valley, the more likely it is to resemble the geomorphological shape of a cirque. In glacial valleys or trough valleys, it may be referred to as the trough head or trough end.
In mountains with predominantly crystalline rock the heads of the valleys are generally very wet, sometimes boggy and often support lush alpine meadows, whilst those made of limestone are usually dry and covered in talus or gravel. Where there has been ice age glaciation, the valley bottoms are modified by moraines and mountain lakes are common.
== See also ==
Structural basin
U-shaped or trough valley
Landform
Valley step
== References ==
== Bibliography ==
Leser, Hartmut, ed. (2005). Wörterbuch Allgemeine Geographie, 13th ed., dtv, Munich, ISBN 978-3-423-03422-7.

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Height above mean sea level is a measure of a location's vertical distance (height, elevation or altitude) in reference to a vertical datum based on a historic mean sea level. In geodesy, it is formalized as orthometric height. The zero level varies in different countries due to different reference points and historic measurement periods. Climate change and other forces can cause sea levels and elevations to vary over time.
== Uses ==
Elevation or altitude above sea level is a standard measurement for:
Geographic locations such as towns, mountains and other landmarks.
The top of buildings and other structures.
Mining infrastructure, particularly underground.
Flying objects such as airplanes or helicopters below a transition altitude defined by local regulations.
== Units and abbreviations ==
Elevation or altitude is generally expressed as "metres above mean sea level" in the metric system, or "feet above mean sea level" in United States customary and imperial units. Common abbreviations in English are:
AMSL – above mean sea level
AOD or AODN – above ordnance datum
ASL – above sea level
FAMSL – feet above mean sea level
FASL – feet above sea level
MAMSL – metres above mean sea level
MASL – metres above sea level
MSL – mean sea level
For elevations or altitudes, often just the abbreviation MSL is used, e.g., Mount Everest (8849 m MSL), or the reference to sea level is omitted completely, e.g., Mount Everest (8849 m).
== Methods of measurement ==
Altimetry is the measurement of altitude or elevation above sea level. Common techniques are:
Surveying, especially levelling.
Global Navigation Satellite System (such as GPS), where a receiver determines a location from pseudoranges to multiple satellites. A geoid is needed to convert the 3D position to sea-level elevation.
Pressure altimeter measuring atmospheric pressure, which decreases as altitude increases. Since atmospheric pressure varies with the weather, too, a recent local measure of the pressure at a known altitude is needed to calibrate the altimeter.
Stereoscopy in aerial photography.
Aerial lidar and satellite laser altimetry.
Aerial or satellite radar altimetry.
Accurate measurement of historical mean sea levels is complex. Land mass subsidence (as occurs naturally in some regions) can give the appearance of rising sea levels. Conversely, markings on land masses that are uplifted (due to geological processes) can suggest a relative lowering of mean sea level.
== See also ==
Depth below seafloor
Height above average terrain
Height above ground level
List of places on land with elevations below sea level
Ordnance datum
== References ==

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The term hermit kingdom is an epithet used to refer to any country, organization or society that willfully isolates itself off, either metaphorically or physically, from the rest of the world. North Korea is the most commonly cited example of a hermit kingdom-like country due to its Juche state ideology which is heavily focused on isolationist and self-sufficient internal politics. Other less prominent quoted examples are Turkmenistan, Eritrea, and Bhutan.
== North Korea ==
The first country to be described as a "hermit kingdom" was Korea during the Joseon dynasty, in William Elliot Griffis's 1882 book Korea: The Hermit Nation.
Korea, which had become increasingly isolationist since the 17th century, was frequently described as a hermit kingdom until 1905, when it became a protectorate of Japan. Today, historical Korea is split into South Korea and North Korea, two states with starkly contrasting economic ideologies. Whereas South Korea is a major developed economy and trade-dependent economy as well as a major importer of overseas goods, North Korea pursues a largely isolationist state ideology known as Juche with a planned economy.
== Cold War uses ==
During the Cold War, Enver Hoxha's Albania was widely considered a "hermit kingdom" as it was a Stalinist regime, did not allow its ordinary citizens out of the country, and pursued autarky to become entirely self-sufficient. Unlike North Korea, Hoxha's regime, after the Sino-Albanian split, refused to ally with anyone and was hostile towards the entire world, which made it more isolationist than North Korea, which was then Stalinist but was allied with other Eastern Bloc states and did not become isolationist until after the end of the Cold War.
== Modern use ==
Today, the term is often applied to North Korea in news and social media, and in 2009, it was used by Hillary Clinton, then the United States Secretary of State.
Other current countries considered isolationist "hermit kingdoms" include Turkmenistan,
Belarus,
Eritrea,
and the Islamic Emirate of Afghanistan.
Historically, the term has been applied to Nepal,
Ladakh,
and Bhutan
in the Himalayas.
== Other uses ==
The term "hermit kingdom" has also been used to describe Western Australia when it closed its borders during the COVID-19 pandemic.
== See also ==
Haijin – Isolationist policy in early modern China
Sakoku – Japanese isolationist policy from 1633–1853
Kim Il Sung – Leader of North Korea from 1948 to 1994
Isolationism – Policy against engaging in international relations
== References ==
== Further reading ==
Fischer, David Hackett (1970). Historians' Fallacies: Toward a Logic of Historical Thought. Harper Perennial. ISBN 0-06-131545-1.
Seth, Michael J. (Fall 2008). "Korea: From Hermit Kingdom to Colony". Association for Asian Studies. 13 (2: Asia in World History: 1750-1914): 28–33. Retrieved October 8, 2024.

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Hinterland is the area under the influence of a particular human settlement. The word comes from a German word meaning 'land behind' a city, a port, or similar. Its use in English was first documented by the geographer George Chisholm in his Handbook of Commercial Geography (1888). Originally the term was associated with the area of a port in which materials for export and import are stored and shipped. Subsequently, the use of the word expanded to its current use.
== History ==
The word hinterland was recorded in English was by Scottish geographer George Chisholm in 1888, to describe the region behind a port that was economically connected to it for imports and exports. The term was later adopted during the era of European colonialism, particularly during the Scramble for Africa to refer to inland areas that coastal powers claimed as their own.
== Geographic region ==
An area behind a coast or the shoreline of a river. Specifically, by the doctrine of the hinterland, the hinterland is the inland region lying behind a port and is claimed by the state that owns the coast.
In shipping usage, a port's hinterland is the area that it serves, both for imports and for exports.
The term is also used to refer to the area around a city or town.
More generally, hinterland can refer to the rural area economically tied to an urban catchment area. The size of a hinterland can depend on geography, or on the ease, speed, and cost of transportation between the catchment area and the hinterland.
In colonial usage, the term was applied to the surrounding areas of former European colonies in Africa, which, although not part of the colony itself, were influenced by the colony. By analogous general economic usage, hinterland can refer to the area surrounding a service from which customers are attracted, also called the market area.
In German, Hinterland is sometimes used more generally to describe any sparsely populated area where the infrastructure is underdeveloped, although Provinz (analogous to province) is more common. In the United States, and particularly in the American Midwest (a region of German cultural heritage located far from ocean ports), it is this meaning and not the one relating to ports that predominates in common use. Analogous terms include "the countryside", "the sticks", "the boonies", backcountry, boondocks, the Bush (in Alaskan usage), the outback (Australia), and the sertão (Brazil).
In Germany a local area in the western part of the Kurfürstentum Hessen (Electorate of Hesse) is named Hessisches Hinterland (short: Hinterland, Hessian Hinterland) without being the local backcountry to a larger city. Cities there are Battenberg, Biedenkopf and Gladenbach. The name Hinterland was in use over many centuries, and nowadays means a smaller area. Lesser known, similar names are given to other areas in Germany (and Switzerland).
In Italy, hinterland is used to describe the metropolitan area of a city, especially Milan, outside of the main municipality.
== Breadth of knowledge ==
A further sense in which the term is commonly applied, especially by British politicians, is in talking about an individual's depth and breadth of knowledge (or lack thereof), of matters outside politics, specifically of academic, artistic, cultural, literary and scientific pursuits. For instance, one could say, "X has a vast hinterland", or "Y has no hinterland". The spread of this usage is usually credited to Denis Healey (British Defence Secretary 1964–1970, Chancellor of the Exchequer 1974–1979) and his wife Edna Healey, initially in the context of the lack of hinterland—i.e., interests outside of politics—of former Prime Minister Margaret Thatcher.
== See also ==
Dalmatian Hinterland
== References ==

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A honeypot site is a location attractive to tourists who, due to their numbers, place pressure on the environment and local people. Honeypots are often used by cities or countries to manage their tourism industry.
The use of honeypots can protect fragile land away from major cities while satisfying tourists. One such example is the establishment of local parks to prevent tourists from damaging more valuable ecosystems further from their main destination. Honeypots have the added benefit of concentrating many income-generating visitors in one place, therefore developing that area, and in turn making it more appealing to tourists. However, honeypots can suffer from problems of overcrowding, including litter, vandalism, and strain on facilities and transport networks.
Honeypots attract tourists due to parking spaces, shopping centres, public parks, and public toilets. The tourist shops are normally placed all over the shopping centre, which creates pressure on the whole centre to keep the area looking tidy. For example, Stratford-upon-Avon has shops that are aimed mostly at tourists. On a particular street, five shops were aimed towards the locals, and ten shops catered to tourists, reflecting the business opportunity that tourism presents for shopkeepers and other businesspeople in the local economy.
The once sleepy medieval village has attracted an increasing number of visitors over recent years and is a classic example of a tourist 'honeypot' ... Ste. Enimie is one of these 'designated' places that are designed to attract people to it and therefore reduce the impact on the surrounding area.
== See also ==
Tourist city
== References ==

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In general, an imaginary line is usually any sort of geometric line (more generally, curves) that has only an abstract definition and does not physically exist. They are often used to properly identify places on a map.
Some outside geography do exist. A centerline is a nautical term for a line down the center of a vessel lengthwise.
== Examples ==
=== Geography ===
As a geographical concept, an imaginary line may serve as an arbitrary division, such as
Antarctic Circle
Arctic Circle
Border
International Date Line
Latitude, including the Equator, the Tropic of Capricorn and the Tropic of Cancer
Longitude, the Prime Meridian Any axis about which an object spins is an imaginary line.
Mason–Dixon line, which informally marks pieces of the borders of four U.S. states: Delaware, Maryland, Pennsylvania, and West Virginia, once part of Virginia. Symbolically, the line separates the Northern United States from the Southern United States
Missouri Compromise Line
Time zones
=== Science and engineering ===
Line of sight
Optical ray
Force lines in mechanical and structural engineering
Field lines for electric and magnetic fields
== See also ==
Imaginary line (mathematics)
== References ==
== External links ==
World Geography Glossary

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Information grazing refers to the ability to quickly obtain knowledge and facts just in time to solve new problems or answer questions. "Information grazing" can also be "information jumping", jumping from site to site and cherry-picking information seems to "rewire" the brain to deleterious effects or focus on something long enough to fully understand all its implications.
Unlike traditional learning, where learning a subject in depth was necessary to draw enough pertinent knowledge to solve new problems or answer questions, information grazing assumes some subjects are so large, fast-changing, interdependent, or esoteric, that traditional methods of learning may be unable to solve new problems or answer questions as efficiently. Information grazing is also one of the most commonly used coping techniques for stress and experts have noticed a trend with people many under the age of 35.
The change from a traditional in-depth learning and memorizing of facts to a mentality of quickly finding, using, and then forgetting knowledge, stems from the technological singularity concept that information is growing so fast (see information explosion or information overload) that an individual can no longer hope to be a "renaissance man" or effectively keep up with some fields of knowledge. Examples of fields of knowledge that are more susceptible to information grazing techniques are science, medical, and engineering, where the “newest” knowledge has become so dynamic, that documentation and dissemination has increasingly moved from fixed paper media to digital formats allowing easier updating and searchability using tools such as AI. With the advent of the Internet and modern computer-cataloging of libraries, vast sums of knowledge are easily accessible in overwhelming quantities in real time. And, with expected future advances in search engine technology and library services, the trend of information overload is expected to worsen; information grazing techniques will become more prevalent to deal with the overload.
Disadvantages of information grazing come from its advantages. Switching from a "fixed" source of information that is constant, verifiable, and worth memorizing to "fluid" sources that are always in flux can lead to quick solutions that are unverified or worse, incorrect. Studies have shown that many people don't read past the first sentences of a Web site's content, and many never go beyond the first ten links listed in a search. As information becomes more like an instantaneous consumable item, memorization is less fact-based but more procedural (i.e. how to find it). Similar concepts are found in Japanese education where after intense study of many unconnected facts, most of the information is forgotten or if remembered, not connected to other relevant facts. In the US, this is similar to cramming an exam. Information grazing may have the same effect but greater, since it is done over the period of years.
== See also ==
SparkNotes, often used to "read" books in a few minutes.
Browsing
The Cult of the Amateur
Is Google Making Us Stupid?
Large language model
== References ==
== External links ==
Growing Up Online "Frontline" Jan 2008. The sections on school work and report writing.
Digital Nation "Frontline" Feb 2011. The sections on students and learning.
The Evolution of Information Grazing on Bokardo.com

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Intermontane is a physiographic adjective formed from the prefix "inter-" (signifying among, between, amid, during, within, mutual, reciprocal) and the adjective "montane" (inhabiting, or growing in mountainous regions, especially cool, moist upland slopes below the timberline).
The corresponding physiographic noun is intermountain, while the noun intermontane is an ecologic noun meaning among, between, amid, or within "flora and fauna of a montane habitat." As an example, an alpine region would be an intermontane for a species that migrates between a glacial region and a subalpine region.
== Use of the term ==
Intermontane Basin, a wide valley between mountain ranges that is partly filled with alluvium such as New Zealand's Mackenzie Basin.
Intermontane Belt, a physiogeological region in the North American Pacific Northwest.
Intermontane Plateaus, the United States physiographic region of the Intermountain West.
Intermontane Steppe, a term used mainly in reference to the Sayan Intermontane Steppe.
In palaeogeography, intermontane may refer to
Intermontane Islands, an ancient Pacific Ocean chain of volcanic islands of the Intermontane Plate that were active during the Triassic period.
Intermontane Plate, an ancient oceanic tectonic plate on the west coast of North America about 195 million years ago.
Intermontane Trench, an ancient oceanic trench of the Triassic period along the west coast of North America in the former Slide Mountain Ocean.
== References ==
== External links ==
The Intermontane Basins and Plateaus

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The Intertropical Convergence Zone (ITCZ ITCH, or ICZ), known by sailors as the doldrums or the calms because of its monotonous windless weather, is the area where the northeast and the southeast trade winds converge. It encircles Earth near the thermal equator, though its specific position varies seasonally. When it lies near the geographic equator, it is called the near-equatorial trough. Where the ITCZ is drawn into and merges with a monsoonal circulation, it is sometimes referred to as a monsoon trough (a usage that is more common in Australia and parts of Asia).
== Meteorology ==
The ITCZ was originally identified from the 1920s to the 1940s as the Intertropical Front (ITF); however, after the recognition of the significance of wind field convergence in tropical weather production in the 1940s and 1950s, the term Intertropical Convergence Zone (ITCZ) was then applied.
The ITCZ appears as a band of clouds, typically thunderstorms, that encircle the globe near the Equator. In the Northern Hemisphere, the trade winds move in a southwestward direction from the northeast, while in the Southern Hemisphere, they move northwestward from the southeast. When the ITCZ is positioned north or south of the Equator, these directions change according to the Coriolis effect imparted by Earth's rotation. For instance, when the ITCZ is situated north of the Equator, the southeast trade wind changes to a southwest wind as it crosses the Equator. The ITCZ is formed by vertical motion largely appearing as convective activity of thunderstorms driven by solar heating, which effectively draw air in; these are the trade winds. The ITCZ is effectively a tracer of the ascending branch of the Hadley cell and is wet. The dry descending branch is the horse latitudes.
The location of the ITCZ gradually varies with the seasons, roughly corresponding with the location of the thermal equator. As the heat capacity of the oceans is greater than air over land, migration is more prominent over land. Over the oceans, where the convergence zone is better defined, the seasonal cycle is more subtle, as the convection is constrained by the distribution of ocean temperatures. Sometimes, a double ITCZ forms, with one located north and another south of the Equator, one of which is usually stronger than the other. When this occurs, a narrow ridge of high pressure forms between the two convergence zones.
== ITCZ over oceans vs. land ==
The ITCZ is commonly defined as an equatorial zone where the trade winds converge. Rainfall seasonality is traditionally attributed to the north–south migration of the ITCZ, which follows the sun. Although this is largely valid over the equatorial oceans, the ITCZ and the region of maximum rainfall can be decoupled over the continents. The equatorial precipitation over land is not simply a response to just the surface convergence. Rather, it is modulated by a number of regional features such as local atmospheric jets and waves, proximity to the oceans, terrain-induced convective systems, moisture recycling, and spatiotemporal variability of land cover and albedo.
== South Pacific convergence zone ==
The South Pacific convergence zone (SPCZ) is a reverse-oriented, or west-northwest to east-southeast aligned, trough extending from the west Pacific warm pool southeastwards towards French Polynesia. It lies just south of the equator during the Southern Hemisphere warm season, but can be more extratropical in nature, especially east of the International Date Line. It is considered the largest and most important piece of the ITCZ, and has the least dependence upon heating from a nearby land mass during the summer than any other portion of the monsoon trough. The southern ITCZ in the eastern tropical Pacific and southern tropical Atlantic, known as the SITCZ, occurs during the Southern Hemisphere fall between 3° and 10° south of the equator east of the 140th meridian west longitude during cool or neutral El Niño–Southern Oscillation (ENSO) patterns. When ENSO reaches its warm phase, otherwise known as El Niño, the tongue of lowered sea surface temperatures due to upwelling off the South American continent disappears, which causes this convergence zone to vanish as well.
== Effects on weather ==
Variation in the location of the intertropical convergence zone drastically affects rainfall in many equatorial nations, resulting in the wet and dry seasons of the tropics rather than the cold and warm seasons of higher latitudes. Longer term changes in the intertropical convergence zone can result in severe droughts or flooding in nearby areas.
In some cases, the ITCZ may become narrow, especially when it moves away from the equator; the ITCZ can then be interpreted as a front along the leading edge of the equatorial air. There appears to be a 15 to 25-day cycle in thunderstorm activity along the ITCZ, which is roughly half the wavelength of the Madden–Julian oscillation (MJO).
Within the ITCZ the average winds are slight, unlike the zones north and south of the equator where the trade winds feed. As trans-equator sea voyages became more common, sailors in the eighteenth century named this belt of calm the doldrums because of the calm, stagnant, or inactive winds.
== Role in tropical cyclone formation ==
Tropical cyclogenesis depends upon low-level vorticity as one of its six requirements, and the ITCZ fills this role as it is a zone of wind change and speed, otherwise known as horizontal wind shear. As the ITCZ migrates to tropical and subtropical latitudes and even beyond during the respective hemisphere's summer season, increasing Coriolis force makes the formation of tropical cyclones within this zone more possible. Surges of higher pressure from high latitudes can enhance tropical disturbances along its axis. In the tropical north Atlantic and the eastern portion of the tropical north Pacific oceans, tropical waves move along the axis of the ITCZ causing an increase in thunderstorm activity, and clusters of thunderstorms can develop under weak vertical wind shear.

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== Hazards ==
In the Age of Sail, to find oneself becalmed in this region in a hot and muggy climate could mean death when wind was the only effective way to propel ships across the ocean. Calm periods within the doldrums could strand ships for days or weeks. Even today, leisure and competitive sailors attempt to cross the zone as quickly as possible as the erratic weather and wind patterns may cause unexpected delays.
In 2009, thunderstorms along the Intertropical Convergence Zone played a role in the loss of Air France Flight 447, which crashed while flying from Rio de Janeiro–Galeão International Airport to Charles de Gaulle Airport near Paris. The aircraft crashed with no survivors while flying through a series of large ITCZ thunderstorms, and ice forming rapidly on airspeed sensors was the precipitating cause for a cascade of human errors which ultimately doomed the flight. Most aircraft flying these routes are able to avoid the larger convective cells without incident.
== Effects of climate change ==
Based on paleoclimate proxies, the position and intensity of the ITCZ varied in prehistoric times along with changes in global climate. During Heinrich events within the last 100 ka, a southward shift of the ITCZ coincided with the intensification of the Northern Hemisphere Hadley cell coincident with weakening of the Southern Hemisphere Hadley cell. The ITCZ shifted north during the mid-Holocene but migrated south following changes in insolation during the late-Holocene towards its current position. The ITCZ has also undergone periods of contraction and expansion within the last millennium. A southward shift of the ITCZ commencing after the 1950s and continuing into the 1980s may have been associated with cooling induced by aerosols in the Northern Hemisphere based on results from climate models; a northward rebound began subsequently following forced changes in the gradient in temperature between the Northern and Southern hemispheres. These fluctuations in ITCZ positioning had robust effects on climate; for instance, displacement of the ITCZ may have led to drought in the Sahel in the 1980s.
Atmospheric convection may become stronger and more concentrated at the center of the ITCZ in response to a globally warming climate, resulting in sharpened contrasts in precipitation between the ITCZ core (where precipitation would be amplified) and its edges (where precipitation would be suppressed). Atmospheric reanalyses suggest that the ITCZ over the Pacific has narrowed and intensified since at least 1979, in agreement with data collected by satellites and in-situ precipitation measurements. The drier ITCZ fringes are also associated with an increase in outgoing longwave radiation outward of those areas, particularly over land within the mid-latitudes and the subtropics. This change in the ITCZ is also reflected by increasing salinity within the Atlantic and Pacific underlying the ITCZ fringes and decreasing salinity underlying central belt of the ITCZ. The IPCC Sixth Assessment Report indicated "medium agreement" from studies regarding the strengthening and tightening of the ITCZ due to anthropogenic climate change.
Less certain are the regional and global shifts in ITCZ position as a result of climate change, with paleoclimate data and model simulations highlighting contrasts stemming from asymmetries in forcing from aerosols, volcanic activity, and orbital variations, as well as uncertainties associated with changes in monsoons and the Atlantic meridional overturning circulation. The climate simulations run as part of Coupled Model Intercomparison Project Phase 5 (CMIP5) did not show a consistent global displacement of the ITCZ under anthropogenic climate change. In contrast, most of the same simulations show narrowing and intensification under the same prescribed conditions. However, simulations in Coupled Model Intercomparison Project Phase 6 (CMIP6) have shown greater agreement over some regional shifts of the ITCZ in response to anthropogenic climate change, including a northward displacement over the Indian Ocean and eastern Africa and a southward displacement over the eastern Pacific and Atlantic oceans.
== In literature ==
The doldrums are notably described in Samuel Taylor Coleridge's poem The Rime of the Ancient Mariner (1798) and also provide a metaphor for the initial state of boredom and indifference of Milo, the child hero of Norton Juster's classic 1961 children's novel The Phantom Tollbooth. It is also cited in the 1939 book Wind, Sand and Stars.
== See also ==
Asymmetry of the Intertropical Convergence Zone
Chemical equator
Monsoon trough
Horse latitudes
Polar front
Roaring Forties
== References ==
== External links ==
The ITCZ in Africa via the University of South Carolina
"A Shifting Band of Rain", Scientific American (March 2011)
Duane E. Waliser and Catherine Gautier, November 1993: "A Satellite-derived Climatology of the ITCZ". J. Climate, 6, 2162–2174.

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In geology, and more specifically in structural geology, a joint is a break (fracture) of natural origin in a layer or body of rock that lacks visible or measurable movement parallel to the surface (plane) of the fracture ("Mode 1" Fracture). Although joints can occur singly, they most frequently appear as joint sets and systems. A joint set is a family of parallel, evenly spaced joints that can be identified through mapping and analysis of their orientations, spacing, and physical properties. A joint system consists of two or more intersecting joint sets.
The distinction between joints and faults hinges on the terms visible or measurable, a difference that depends on the scale of observation. Faults differ from joints in that they exhibit visible or measurable lateral movement between the opposite surfaces of the fracture ("Mode 2" and "Mode 3" Fractures). Thus a joint may be created by either strict movement of a rock layer or body perpendicular to the fracture or by varying degrees of lateral displacement parallel to the surface (plane) of the fracture that remains "invisible" at the scale of observation.
Joints are among the most universal geologic structures, found in almost every exposure of rock. They vary greatly in appearance, dimensions, and arrangement, and occur in quite different tectonic environments. Often, the specific origin of the stresses that created certain joints and associated joint sets can be quite ambiguous, unclear, and sometimes controversial. The most prominent joints occur in the most well-consolidated, lithified, and highly competent rocks, such as sandstone, limestone, quartzite, and granite. Joints may be open fractures or filled by various materials. Joints infilled by precipitated minerals are called veins and joints filled by solidified magma are called dikes.
== Formation ==
Joints arise from brittle fracture of a rock or layer due to tensile stress. This stress may be imposed from outside; for example, by the stretching of layers, the rise of pore fluid pressure, or shrinkage caused by the cooling or desiccation of a rock body or layer whose outside boundaries remained fixed.
When tensional stresses stretch a body or layer of rock such that its tensile strength is exceeded, it breaks. When this happens the rock fractures in a plane parallel to the maximum principal stress and perpendicular to the minimum principal stress (the direction in which the rock is being stretched). This leads to the development of a single sub-parallel joint set. Continued deformation may lead to development of one or more additional joint sets. The presence of the first set strongly affects the stress orientation in the rock layer, often causing subsequent sets to form at a high angle, often 90°, to the first set.
== Types ==
Joints are classified by their geometry or by the processes that formed them.
=== By geometry ===
The geometry of joints refers to the orientation of joints as either plotted on stereonets and rose-diagrams or observed in rock exposures. In terms of geometry, three major types of joints are recognized: columnar jointing, systematic joints, and nonsystematic joints.
==== Columnar ====
Columnar jointing is distinguished by triple joint junction points, which split a rock body into long prisms or columns, hence the name. Typically, the joint planes are oriented at or about 120° angles, and so columns are usually hexagonal in section, although 3-, 4-, 5- and 7-sided columns are relatively common.
Columnar jointing is typical of thick lava flows, and shallow dikes and sills, but rare cases of columnar jointing have also been reported in sedimentary strata.
The width of these prismatic columns ranges from a few centimeters to several metres, and they are often oriented perpendicular to surfaces of contact between the igneous rock and its cooler surroundings. They can thus usually be seen at the top and base surfaces of lava flows, and the contacts of tabular igneous intrusions with the surrounding rock.
Columnar jointing is also known as either columnar structure, prismatic joints, or prismatic jointing
==== Systematic ====
Systematic joints are planar, parallel, joints that can be traced for some distance, and occur at regularly, evenly spaced distances on the order of centimeters, meters, tens of meters, or even hundreds of meters. As a result, they occur as families of joints that form recognizable joint sets. Typically, exposures or outcrops within a given area or region of study contains two or more sets of systematic joints, each with its own distinctive properties such as orientation and spacing, that intersect to form well-defined joint systems.
Based upon the angle at which joint sets of systematic joints intersect to form a joint system, systematic joints can be subdivided into conjugate and orthogonal joint sets. The angles at which joint sets within a joint system commonly intersect are called dihedral angles by structural geologists. When the dihedral angles are nearly 90° within a joint system, the joint sets are known as orthogonal joint sets. When the dihedral angles are from 30 to 60° within a joint system, the joint sets are known as conjugate joint sets.
Within regions that have experienced tectonic deformation, systematic joints are typically associated with either layered or bedded strata that have been folded into anticlines and synclines. Such joints can be classified according to their orientation in respect to the axial planes of the folds as they often commonly form in a predictable pattern with respect to the hinge trends of folded strata. Based upon their orientation to the axial planes and axes of folds, the types of systematic joints are:
Longitudinal joints – Joints which are roughly parallel to fold axes and often fan around the fold.
Cross-joints – Joints which are approximately perpendicular to fold axes.
Diagonal joints – Joints which typically occur as conjugate joint sets that trend oblique to the fold axes.
Strike joints – Joints which trend parallel to the strike of the axial plane of a fold.
Cross-strike joints – Joints which cut across the axial plane of a fold.

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==== Nonsystematic ====
Nonsystematic joints are joints that are so irregular in form, spacing, and orientation that they cannot be readily grouped into distinctive, through-going joint sets.
=== By formation ===
Joints can be classified according to their origin, under the labels of tectonics, hydraulics, exfoliation, unloading (release), and cooling. Different authors have proposed contradictory hypotheses for the same joint sets and types. And, joints in the same outcrop may form at different times under varied circumstances.
==== Tectonic ====
Tectonic joints are joints formed when the relative displacement of the joint walls is normal to its plane as the result of brittle deformation of bedrock in response to regional or local tectonic deformation of bedrock. Such joints form when directed tectonic stress causes the tensile strength of
bedrock to be exceeded as the result of the stretching of rock layers under conditions of elevated pore fluid pressure and directed tectonic stress. Tectonic joints often reflect local tectonic stresses associated with local folding and faulting. Tectonic joints occur as both nonsystematic and systematic joints, including orthogonal and conjugate joint sets.
==== Hydraulic ====
Hydraulic joints are formed when pore fluid pressure becomes elevated as a result of vertical gravitational loading. In simple terms, the accumulation of either sediments, volcanic, or other material causes an increase in the pore pressure of groundwater and other fluids in the underlying rock when they cannot move either laterally or vertically in response to this pressure. This also causes an increase in pore pressure in preexisting cracks that increases the tensile stress on them perpendicular to the minimum principal stress (the direction in which the rock is being stretched). If the tensile stress exceeds the magnitude of the least principal compressive stress the rock will fail in a brittle manner and these cracks propagate in a process called hydraulic fracturing. Hydraulic joints occur as both nonsystematic and systematic joints, including orthogonal and conjugate joint sets. In some cases, joint sets can be a tectonic - hydraulic hybrid.
==== Exfoliation ====
Exfoliation joints are sets of flat-lying, curved, and large joints that are restricted to massively exposed rock faces in a deeply eroded landscape. Exfoliation jointing consists of fan-shaped fractures varying from a few meters to tens of meters in size that lie sub-parallel to the topography. The vertical, gravitational load of the mass of a mountain-size bedrock mass drives longitudinal splitting and causes outward buckling toward the free air. In addition, paleostress sealed in the granite before the granite was exhumed by erosion and released by exhumation and canyon cutting is also a driving force for the actual spalling.
==== Unloading ====
Unloading joints or release joints arise near the surface when bedded sedimentary rocks are brought closer to the surface during uplift and erosion; when they cool, they contract and become relaxed elastically. A stress builds up which eventually exceeds the tensile strength of the bedrock and results in jointing. In the case of unloading joints, compressive stress is released either along preexisting structural elements (such as cleavage) or perpendicular to the former direction of tectonic compression.
==== Cooling ====
Cooling joints are columnar joints that result from the cooling of either lava from the exposed surface of a lava lake or flood basalt flow or the sides of a tabular igneous, typically basaltic, intrusion. They exhibit a pattern of joints that join together at triple junctions either at or about 120° angles. They split a rock body into long, prisms or columns that are typically hexagonal, although 3-, 4-, 5- and 7-sided columns are relatively common. They form as a result of a cooling front that moves from some surface, either the exposed surface of a lava lake or flood basalt flow or the sides of a tabular igneous intrusion into either lava of the lake or lava flow or magma of a dike or sill.
== Fractography ==
Joint propagation can be studied through the techniques of fractography in which characteristic marks such as hackles and plumose structures are used to determine propagation directions and, in some cases, the principal stress orientations.
== Shear fractures ==
Some fractures that look like joints are actually shear fractures, which in effect are microfaults. They do not form as the result of the perpendicular opening of a fracture due to tensile stress, but through the shearing of fractures that causes lateral movement of the faces. Shear fractures can be confused with joints because the lateral offset of the fracture faces is not visible in the outcrop or in a specimen. Because of the absence of diagnostic ornamentation or the lack of any discernible movement or offset, they can be indistinguishable from joints. Such fractures occur in planar parallel sets at an angle of 60 degrees and can be of the same size and scale as joints. As a result, some "conjugate joint sets" might actually be shear fractures. Shear fractures are distinguished from joints by the presence of slickensides, the products of shearing movement parallel to the fracture surface. The slickensides are fine-scale, delicate ridge-in-groove lineations on the surface of fracture surfaces.

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== Importance ==
Joints are important not only in understanding the local and regional geology and geomorphology but also in developing natural resources, in the safe design of structures, and in environmental protection. Joints have a profound control on weathering and erosion of bedrock. As a result, they exert a strong control on how topography and morphology of landscapes develop. Understanding the local and regional distribution, physical character, and origin of joints is a significant part of understanding the geology and geomorphology of an area. Joints often impart a well-develop fracture-induced permeability to bedrock. As a result, joints strongly influence, even control, the natural circulation (hydrogeology) of fluids, e.g. groundwater and pollutants within aquifers, petroleum in reservoirs, and hydrothermal circulation at depth, within bedrock. Thus, joints are important to the economic and safe development of petroleum, hydrothermal, and groundwater resources and the subject of intensive research relative to these resources. Regional and local joint systems exert a strong control on how ore-forming hydrothermal fluids (consisting largely of H2O, CO2, and NaCl — which formed most of Earth's ore deposits) circulated within its crust. As a result, understanding their genesis, structure, chronology, and distribution is an important part of finding and profitably developing ore deposits. Finally, joints often form discontinuities that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel, foundation, or slope construction. As a result, joints are an important part of geotechnical engineering in practice and research.
== Image gallery ==
== See also ==
Basalt fan structure – Formation of columnar jointed igneous rock
Exfoliating granite – Granite spalling in superficial layers due to tempearature cycles
Tessellated pavement – Flat rock surface subdivided by fractures
== References ==
== External links ==
Aydin, A., and J. Zhong (nda) Non-orthogonal Joint Sets, Multiple Joint Sets, Rock Fracture Knowledgebase, Stanford University, Stanford, California.
Aydin, A., and J. Zhong (ndb) Orthogonal Joint Sets, Multiple Joint Sets, Rock Fracture Knowledgebase, Stanford University, Stanford, California.
Aydin, A., and J. Zhong (ndb) Patterns of Multiple Joint Sets, Multiple Joint Sets, Rock Fracture Knowledgebase, Stanford University, Stanford, California.

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Knowledge organization system (KOS), concept system, or concept scheme is the generic term used in knowledge organization (KO) for the selection of concepts with an indication of selected semantic relations. Despite their differences in type, coverage, and application, all KOS aim to support the organization of knowledge and information to facilitate their management and retrieval.
KOS vary in complexity from simple sorted lists to complex relational networks. They represent both structural and functional features, and serve to eliminate ambiguity, control synonyms, establish relationships, and present properties. From their origins in library and information science (LIS), KOS have been applied to other domains and disciplines within science and industry, although scholarly research and debate remain primarily within the KO field. Challenges of KOS include ambiguity of terminology, repercussions of biased systems, and potential obsolescence.
KOS can be expressed in RDF and RDFS as per the Simple Knowledge Organization System (SKOS) recommendation by W3C, which aims to enable the sharing and linking of KOS via the Web.
One of the largest collections of KOS is the BARTOC registry.
== Types ==
While different schema of KOS have been proposed, most are generally arranged in terms of the complexity of their construction and maintenance. Some scholars argue that organizing KOS on a spectrum oversimplifies the shared characteristics among them, and may even result in a non-ideal structure being chosen.
The following types are not exhaustive, and are often not mutually-exclusive in practice.
=== Term lists ===
Term lists are the least structured form of KOS. They include lists, glossaries, dictionaries, and synonym rings. Authority files and gazetteers may also be considered term lists, however other scholars categorize them and directories as "metadata-like models".
Examples include the Union List of Artist Names name authority file and the GeoNames gazetteer.
=== Categorization and classification ===
KOS that emphasize specific (and often hierarchical) structures include subject headings, taxonomies, categorization schema, and classification schema & systems.
Despite inconsistent use of the terms "categorization" and "classification" in some literature, categorization is generally loosely-assembled grouping schema and may include attributes that are not mutually exclusive (or having fuzzy boundaries), while classification is related to the arrangement of non-overlapping and mutually-exclusive classes.
Classification schema may be universal (such as Dewey Decimal Classification and Information Coding Classification) or domain-specific (such as the National Library of Medicine Classification).
=== Relationship models ===
The types of KOS with greatest complexity and which utilize connections between concepts include thesauri, semantic networks, and ontologies.
One of the most prominent examples of a semantic network is WordNet.
=== Others ===
Certain structures proposed to be considered types of KOS—but are not consistently included in schema—include folksonomies, topic maps, web directory structures, publication organization systems, and bibliometric maps.
Some KOS organize other KOS themselves—for instance, PeriodO is a gazetteer of periodization categories.
== Applications ==
Some early KOS were developed as a support system for abstracting and indexing services to be used by specially-trained searchers. With the growth of information digitization, usability became increasingly accessible, and more complex structures were developed.
Prominent examples of KOS outside of LIS include organism taxonomy in biology, the periodic table of elements in chemistry, SIC and NAICS classification systems for industry & business, and AGROVOC agricultural controlled vocabulary.
== Challenges ==
The study and design of KOS is an ongoing topic of discussion among KO scholars.
=== Terminology ===
[There is] a serious lack of vocabulary control in the literature on controlled vocabulary.
Inconsistency of terminology within the study of KOS is a common issue. For instance, "ontology" is used for both a specific type of KOS as well as a generic term for any KOS. The terms "taxonomy", "classification", and "categorization" are also sometimes used interchangeably.
=== Bias ===
As knowledge can be historically and culturally biased, scholars have also discussed how KOS themselves can perpetuate harmful practices or stereotypes. For example, a number of concerns and criticisms about the classification of mental disorders in the Diagnostic and Statistical Manual of Mental Disorders have been raised, contributing to ongoing revisions.
Ethical and intentional design approaches have been proposed for multi-perspective KOS in efforts to mitigate bias and other harmful practices.
=== Obsolescence ===
The possible obsolescence of the thesaurus and other simpler KOS has been the topic of debate, especially in the face of increasingly complex ontologies, the growing usage of "Google-like retrieval systems", and the move of KO theory and research away from LIS and toward computer science. Supporters of thesauri argue its continued usefulness for metadata enrichment, vocabulary mapping, and web services, as well as its usage in specific domains such as corporate intranets and digital image libraries.
== See also ==
Library classification
Information retrieval
Epistemology
Metadata
== Notes ==
== References ==
Tudhope, D. & Lykke Nielsen, M. (2006). Introduction to special issue: Knowledge Organization Systems and Services. New Review of Hypermedia and Multimedia, 12(1), 3-9. http://www.journalsonline.tandf.co.uk/media/m35eac0c7l6wvk510nr7/contributions/r/0/7/7/r077564631920800.pdf
Zeng, M. L. & Chan, L. M. (2004). Trends and issues in establishing interoperability among knowledge organization systems. Journal for the American Society for Information Science and Technology, 55(5), 377-395.
Networked Knowledge Organization Systems/Services NKOS: https://nkos.slis.kent.edu/
== External links ==
BARTOC
ISKO Encyclopedia of Knowledge Organization

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Land, also known as dry land, ground, or earth, is the solid terrestrial surface of Earth not submerged by the ocean or another body of water. It makes up 29.2% of Earth's surface and includes all continents and islands. Earth's land surface is almost entirely covered by regolith, a layer of rock, soil, and minerals that forms the outer part of the crust. Land plays an important role in Earth's climate system, being involved in the carbon cycle, nitrogen cycle, and water cycle. One-third of land is covered in trees, another third is used for agriculture, and one-tenth is covered in permanent snow and glaciers. The remainder consists of desert, savannah, and prairie.
Land terrain varies greatly, consisting of mountains, deserts, plains, plateaus, glaciers, and other landforms. In physical geology, the land is divided into two major categories: Mountain ranges and relatively flat interiors called cratons. Both form over millions of years through plate tectonics. Streams – a major part of Earth's water cycle – shape the landscape, carve rocks, transport sediments, and replenish groundwater. At high elevations or latitudes, snow is compacted and recrystallized over hundreds or thousands of years to form glaciers, which can be so heavy that they warp the Earth's crust. About 30 percent of land has a dry climate, due to losing more water through evaporation than it gains from precipitation. Since warm air rises, this generates winds, though Earth's rotation and uneven sun distribution also play a part.
Land is commonly defined as the solid, dry surface of Earth. It can also refer to the collective natural resources that the land holds, including rivers, lakes, and the biosphere. Human manipulation of the land, including agriculture and architecture, can also be considered part of land. Land is formed from the continental crust, the layer of rock on which soil, groundwater, and human and other animal activity sits.
Though modern terrestrial plants and animals evolved from aquatic creatures, Earth's first cellular life likely originated on land. Survival on land relies on fresh water from rivers, streams, lakes, and glaciers, which constitute only three percent of the water on Earth. The vast majority of human activity throughout history has occurred in habitable land areas supporting agriculture and various natural resources. In recent decades, scientists and policymakers have emphasized the need to manage land and its biosphere more sustainably, through measures such as restoring degraded soil, preserving biodiversity, protecting endangered species, and addressing climate change.
== Definition ==
Land is often defined as the solid, dry surface of Earth. The word land may also collectively refer the collective natural resources of Earth, including its land cover, rivers, shallow lakes, its biosphere, the lowest layer of the atmosphere (troposphere), groundwater reserves, and the physical results of human activity on land, such as architecture and agriculture. The boundary between land and sea is called the shoreline.
== Etymology ==
The word land is derived from Old English, from the Proto-Germanic word *landą, "untilled land", and then the Proto-Indo-European *lendʰ-, especially in northern regions that were home to languages like Proto-Celtic and Proto-Slavic. Examples include Old Irish land, "land, plot, church building" and Old Irish ithlann, "threshing floor", and Old East Slavic ljadina "wasteland, weeds".
A country or nation may be referred to as the motherland, fatherland, or homeland of its people. Many countries and other places have names incorporating the suffix -land (e.g. England, Greenland, and New Zealand). The equivalent suffix -stan from Indo-Iranian, ultimately derived from the Proto-Indo-Iranian *sthāna-, is also present in many country and location names, such as Pakistan, Afghanistan, and others throughout Central Asia. The suffix is also used more generally, as in Persian rigestân (ریگستان) "place of sand, desert", golestân (گلستان) "place of flowers, garden", gurestân (گورستان) "graveyard, cemetery", and Hindustân (هندوستان) "land of the Indo people".
== Physical science ==
The study of land and its history in general is called geography. Mineralogy is the study of minerals, and petrology is the study of rocks. Soil science is the study of soils, encompassing the sub-disciplines of pedology, which focuses on soil formation, and edaphology, which focuses on the relationship between soil and life.
=== Formation ===

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The earliest material found in the Solar System is dated to 4.5672±0.0006 bya (billion years ago); therefore, Earth itself must have been formed by accretion around this time. The formation and evolution of the Solar System bodies occurred in tandem with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disc, out of which the planets then grow (in tandem with the star). A nebula contains gas, ice grains and dust (including primordial nuclides). In the nebular hypothesis, planetesimals begin to form as particulate matter accumulates by cohesive clumping and then by gravity. The primordial Earth's assembly took 10–20 myr. By 4.54±0.04 bya, the primordial Earth had formed.
Earth's atmosphere and oceans were formed by volcanic activity and outgassing that included water vapour. The origin of the world's oceans was condensation augmented by water and ice delivered by asteroids, protoplanets, and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing while the newly formed Sun was only at 70% luminosity. By 3.5 bya, the Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. The atmosphere and oceans of the Earth continuously shape the land by eroding and transporting solids on the surface.
Earth's crust formed when the molten outer layer of Planet Earth cooled to form a solid mass as the accumulated water vapour began to act in the atmosphere. Once land became capable of supporting life, biodiversity evolved over hundreds of millions of years, expanding continually except when punctuated by mass extinctions.
The two models that explain land mass propose either a steady growth to the present-day forms or, more likely, a rapid growth early in Earth history followed by a long-term steady continental area. Continents are formed by plate tectonics, a process ultimately driven by the continuous loss of heat from the Earth's interior. On time scales lasting hundreds of millions of years, the supercontinents have formed and broken apart three times. Roughly 750 mya (million years ago), one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 mya, then finally Pangaea, which also broke apart 180 mya.
=== Landmasses ===
A continuous area of land surrounded by an ocean is called a landmass. Although it is most often written as one word to distinguish it from the usage "land mass"—the measure of land area—it may also be written as two words. There are four major continuous landmasses on Earth: Africa–Eurasia, America (landmass), Antarctica, and Australia (landmass), which are subdivided into continents. Up to seven geographical regions are commonly regarded as continents. Ordered from greatest to least land area, these continents are Asia, Africa, North America, South America, Antarctica, Europe, and Australia.
=== Terrain ===
Terrain refers to an area of land and its features. Terrain affects travel, mapmaking, ecosystems, and surface water flow and distribution. Over a large area, it can influence climate and weather patterns. The terrain of a region largely determines its suitability for human settlement: flatter alluvial plains tend to have better farming soils than steeper, rockier uplands.
Elevation is defined as the vertical distance between an object and sea level, while altitude is defined as the vertical distance from an object to Earth's surface. The elevation of Earth's land surface varies from the low point of −418 metres (−1,371 feet) at the Dead Sea, to a maximum altitude of 8,848 metres (29,029 feet) at the top of Mount Everest. The mean height of land above sea level is about 797 metres (2,615 feet), with 98.9% of dry land situated above sea level.
Relief refers to the difference in elevation within a landscape; for example, flat terrain would have "low relief", while terrain with a large elevation difference between the highest and lowest points would be deemed "high relief". Most land has relatively low relief. The change in elevation between two points of the terrain is called a slope or gradient. A topographic map is a form of terrain cartography which depicts terrain in terms of its elevation, slope, and the orientation of its landforms. It has prominent contour lines, which connect points of similar elevation, while perpendicular slope lines point in the direction of the steepest slope. Hypsometric tints are colors placed between contour lines to indicate elevation relative to sea level.
A difference between uplands, or highlands, and lowlands is drawn in several earth science fields. In river ecology, "upland" rivers are fast-moving and colder than "lowland" rivers, encouraging different species of fish and other aquatic wildlife to live in these habitats. For example, nutrients are more present in slow-moving lowland rivers, encouraging different species of macrophytes to grow there. The term "upland" is also used in wetland ecology, where "upland" plants indicate an area that is not a wetland. In addition, the term moorland refers to upland shrubland biomes with acidic soils, while heathlands are lowland shrublands with acidic soils.
=== Geomorphology ===

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Geomorphology refers to the study of the natural processes that shape land's surface, creating landforms. Erosion and tectonics, volcanic eruptions, flooding, weathering, glaciation, the growth of coral reefs, and meteorite impacts are among the processes that constantly reshape Earth's surface over geological time.
Erosion transports one part of land to another via natural processes, such as wind, water, ice, and gravity. In contrast, weathering wears away rock and other solid land without transporting the land somewhere else. Natural erosional processes usually take a long time to cause noticeable changes in the landscape—for example, the Grand Canyon was created over the past 70 million years by the Colorado River, which scientists estimate continues to erode the canyon at a rate of 0.3 meters (0.98 feet) every 200 years. However, humans have caused erosion to be 10–40 times faster than normal, causing half the topsoil of the surface of Earth's land to be lost within the past 150 years.
Plate tectonics refers to the theory that Earth's lithosphere is divided into "tectonic plates" that move over the mantle. This results in continental drift, with continents moving relative to each other. The scientist Alfred Wegener first hypothesized the theory of continental drift in 1912. More researchers developed his idea throughout the 20th century into the now widely accepted theory of plate tectonics.
Several key characteristics define the modern understanding of plate tectonics. The place where two tectonic plates meet is called a plate boundary, with different geological phenomena occurring across different kinds of boundaries. For example, at divergent plate boundaries, seafloor spreading is usually seen, in contrast with the subduction zones of convergent or transform plate boundaries.
Earthquakes and volcanic activity are common in all types of boundaries. Volcanic activity refers to any rupture in Earth's surface where magma escapes, therefore becoming lava. The Ring of Fire, containing two-thirds of the world's volcanos, and over 70% of Earth's seismological activity, comprises plate boundaries surrounding the Pacific Ocean.
=== Climate ===
Earth's land interacts with and influences its climate heavily, since the land's surface heats up and cools down faster than air or water. Latitude, elevation, topography, reflectivity, and land use all have varying effects on climate. The latitude of the land will influence how much solar radiation reaches its surface. High latitudes receive less solar radiation than low latitudes. The land's topography is important in creating and transforming airflow and precipitation. Large landforms, such as mountain ranges, can divert wind energy and make air parcels less dense and therefore able to hold less heat. As air rises, this cooling effect causes condensation and precipitation.
Different types of land cover will influence the land's albedo, a measure of the solar radiation that is reflected, rather than absorbed and transferred to Earth. Vegetation has a relatively low albedo, meaning that vegetated surfaces are good absorbers of the sun's energy. Forests have an albedo of 10–15 percent while grasslands have an albedo of 15–20 percent. In comparison, sandy deserts have an albedo of 25–40 percent.
Land use by humans also plays a role in the regional and global climate. Densely populated cities are warmer and create urban heat islands that have effects on the precipitation, cloud cover, and temperature of the region.
== Features ==
A landform is a natural or manmade land feature. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, mountains, canyons, and valleys, as well as shoreline features such as bays, capes, and peninsulas.
=== Coasts and islands ===

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The shoreline is the interface between the land and the ocean. It migrates each day as tides rise and fall and moves over long periods of time as sea levels change. The shore extends from the low tide line to the highest elevation that can be reached by storm waves, and the coast stretches out inland until the point where ocean-related features are no longer found.
When land is in contact with bodies of water, it can be eroded. The weathering of a coastline may be impacted by the tides, caused by changes in gravitational forces on larger bodies of water. Coasts are important zones in natural ecosystems, often home to a wide range of biodiversity. On land, they harbour important ecosystems such as freshwater or estuarine wetlands, which are important for bird populations and other terrestrial animals. In wave-protected areas they harbor saltmarshes, mangroves or seagrasses, all of which can provide nursery habitat for finfish, shellfish, and other aquatic species. Rocky shores are usually found along exposed coasts and provide habitat for a wide range of sessile animals (e.g. mussels, starfish, barnacles) and various kinds of seaweeds. Along tropical coasts with clear, nutrient-poor water, coral reefs can often be found between depths of 1–50 meters (3.3–164.0 ft).
According to a United Nations atlas, 44% of all people live within 150 km (93 mi) of the sea. Because of their importance in society and high concentration of population, the coast is important for major parts of the global food and economic system, and they provide many ecosystem services to humankind. For example, important human activities happen in port cities. Coastal fisheries for commercial, recreational, and subsistence purposes, and aquaculture are major economic activities and provide jobs, livelihoods, and protein for the majority of coastal human populations. Other coastal spaces like beaches and seaside resorts generate economic activity through tourism. Marine coastal ecosystems can also provide protection against sea level rise and tsunamis. In many countries, the coastal mangrove is the primary source of wood for fuel (e.g. charcoal) and building materials. Coastal ecosystems have a much higher capacity for carbon sequestration than many terrestrial ecosystems, and as such can play a critical role in the near future to help mitigate climate change effects by uptake of atmospheric anthropogenic carbon dioxide.
A subcontinental area of land surrounded by water is an island, and a chain of islands is an archipelago. The smaller the island, the larger the percentage of its land area will be adjacent to the water, and subsequently will be coast or beach. Islands can be formed by a variety of processes. The Hawaiian islands, for example, even though they are not near a plate boundary, formed from isolated volcanic activity. Atolls are ring-shaped islands made of coral, created when subsidence causes an island to sink beneath the ocean surface and leaves a ring of reefs around it.
=== Mountains and plateaus ===
Mountains are features that usually rise at least 300 metres (980 ft) higher than the surrounding terrain. The formation of mountain belts is called orogenesis, and results from plate tectonics. For example, where a plate at a convergent plate boundary pushes one plate above the other, mountains could be formed by either collisional events, such that Earth's crust is pushed upwards, or subductional events, where Earth's crust is pushed into the mantle, causing the crust to melt, rise due to its low density, and solidify into hardened rock, thickening the crust.
A plateau, also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side, creating steep cliffs or escarpments. Both volcanic activity such as the upwelling of magma and extrusion of lava, or erosion of mountains caused from water, glaciers, or aeolian processes, can create plateaus. Plateaus are classified according to their surrounding environment as intermontane, piedmont, or continental. A few plateaus may have a small flat top while others are wider. Buttes are smaller, with less extrusive and more intrusive igneous rock, while plateaus or highlands are the widest, and mesas are a general-sized plateau with horizontal bedrock strata.
=== Plains and valleys ===
Wide, flat areas of land are called plains, which cover more than one-third of Earth's land area. When they occur as lowered areas between mountains, they can create valleys, canyons or gorges, and ravines. A plateau can be thought of as an elevated plain. Plains are known to have fertile soils and be important for agriculture due to their flatness supporting grasses suitable for livestock and facilitating the harvest of crops. Floodplains provided agricultural land for some of the earliest civilizations. Erosion is often a main driver for the creation of plains and valleys, with rift valleys being a noticeable exception. Fjords are glacial valleys that can be thousands of meters deep, opening out to the sea.
=== Caves and craters ===
Any natural void in the ground which can be entered by a human can be considered a cave. They have been important to humans as a place of shelter since the dawn of humanity.
Craters are depressions in the ground, but unlike caves, they do not provide shelter or extend underground. There are many kinds of craters, such as impact craters, volcanic calderas, and isostatic depressions. Karst processes can create both solution caves, the most frequent cave type, and craters, as seen in karst sinkholes.
== Layers ==
The pedosphere is the outermost layer of Earth's continental surface and is composed of soil and subject to soil formation processes. Below it, the lithosphere encompasses both Earth's crust and the uppermost layer of the mantle. The lithosphere rests, or "floats", on top of the mantle below it via isostasy. Above the solid ground, the troposphere and humans' use of land can be considered layers of the land.
=== Land cover ===

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Land cover refers to the material physically present on the land surface, for example, woody crops, herbaceous crops, barren land, and shrub-covered areas. Artificial surfaces (including cities) account for about a third of a percent of all land. Land use refers to human allocation of land for various purposes, including farming, ranching, and recreation (e.g. national parks); worldwide, there are an estimated 16.7 million km2 (6.4 million sq mi) of cropland, and 33.5 million km2 (12.9 million sq mi) of pastureland.
Land cover change detection using remote sensing and geospatial data provides baseline information for assessing the climate change impacts on habitats and biodiversity, as well as natural resources, in the target areas. Land cover change detection and mapping is a key component of interdisciplinary land change science, which uses it to determine the consequences of land change on climate. Land change modeling is used to predict and analyze changes in land cover and use.
=== Soil ===
Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution). Accordingly, soil is a three-state system of solids, liquids, and gases. Soil is a product of several factors: the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time. It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering and erosion.
Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, and a medium for plant growth, making it a critically important provider of ecosystem services. Since soil has a tremendous range of available niches and habitats, it contains a prominent part of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial and largely still unexplored.
Soil is a major component of the Earth's ecosystem. The world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, with effects ranging from ozone depletion and global warming to rainforest destruction and water pollution. With respect to Earth's carbon cycle, soil acts as an important carbon reservoir, and it is potentially one of the most reactive to human disturbance and climate change. As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback (amplification). This prediction has, however, been questioned on consideration of more recent knowledge on soil carbon turnover.
=== Continental crust ===
Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is richer in aluminium silicate and has a lower density compared to the oceanic crust, called sima which is richer in magnesium silicate. Changes in seismic wave velocities have shown that at a certain depth (the Conrad discontinuity), there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character.
The composition of land is not uniform across the Earth, varying between locations and between strata within the same location. The most prominent components of upper continental crust include silicon dioxide, aluminium oxide, and magnesium. The continental crust consists of lower density material such as the igneous rocks granite and andesite. Less common is basalt, a denser volcanic rock that is the primary constituent of the ocean floors. Sedimentary rock is formed from the accumulation of sediment that becomes buried and compacted together. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form about 5% of the crust.
The most abundant silicate minerals on Earth's surface include quartz, feldspars, amphibole, mica, pyroxene and olivine. Common carbonate minerals include calcite (found in limestone) and dolomite. The rock that makes up land is thicker than oceanic crust, and it is far more varied in terms of composition. About 31% of this continental crust is submerged in shallow water, forming continental shelves.
== Life science ==
Land provides many ecosystem services, such as mitigating climate change, regulating water supply through drainage basins and river systems, and supporting food production. Land resources are finite, which has led to regulations intended to safeguard these ecosystem services, and a set of practices called sustainable land management.
=== Land biomes ===
A biome is an area "characterized by its vegetation, soil, climate, and wildlife." There are five major types of biomes on land: grasslands, forests, deserts, tundras, and freshwater. Other types of biomes include shrublands, wetlands, and polar ice caps. An ecosystem refers to the interaction between organisms within a particular environment, and a habitat refers to the environment where a given species or population of organisms lives. Biomes may span more than one continent, and contain a variety of ecosystems and habitats.

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Deserts have an arid climate, generally defined to mean that they receive less than 25 centimetres (9.8 in) of precipitation per year. They make up around one fifth of the Earth's land area, are found on every continent, and can be very hot or very cold (see polar desert). They are home to animals and plants which evolved to be tolerant of droughts. In deserts, most erosion is caused by running water, usually during violent thunderstorms, which cause flash floods. Deserts are expanding due to desertification, which is caused by excessive deforestation and overgrazing.
Tundra is a biome where tree growth is hindered by frigid temperatures and short growing seasons. There are types of tundra associated with different regions: Arctic tundra, alpine tundra, and Antarctic tundra.
A forest is an area of land dominated by trees. Many definitions of "forest" are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' Food and Agriculture Organization (FAO) defines a forest as: "land spanning more than 0.5 hectares with trees higher than 5 meters and a canopy cover of more than 10 per cent, or trees able to reach these thresholds in situ. It does not include land that is predominantly under agricultural or urban use." Types of forests include rainforests, deciduous forests, and boreal forests.
Grasslands are areas where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found, along with variable proportions of legumes like clover and other herbs. Grasslands occur naturally on all continents except Antarctica and are found in most ecoregions of the Earth. Furthermore, grasslands are one of the largest biomes on earth and dominate the landscape worldwide. Types include natural, semi-natural, and agricultural grasslands. Savannas are grasslands with occasional, scattered trees.
=== Fauna and flora ===
Land plants evolved from green algae, and are called embryophytes. They include trees, shrubs, ferns, grass, moss, and flowers. Most plants are vascular plants, meaning that their tissues distribute water and minerals throughout the plant. Through photosynthesis, most plants nourish themselves from sunlight and water, breathing in carbon dioxide and breathing out oxygen. Between 20 and 50% of oxygen is produced by land vegetation.
Unlike plants, terrestrial animals are not a monophyletic group—that is, a group including all terrestrial animals does not encompass all lineages from a common ancestor. This is because there are organisms, such as the whale, that evolved from terrestrial mammals back to an aquatic lifestyle. Many megafauna of the past, such as non-avian dinosaurs, have become extinct due to extinction events, e.g. the Quaternary extinction event.
== Humans and land ==
Land is "deeply intertwined with human development." It is a crucial resource for human survival, humans depend on land for subsistence, and can develop strong symbolic attachments to it. Access to land can determine "survival and wealth," particularly in developing countries, giving rise to complex power relationships in production and consumption. Most of the world's philosophies and religions recognize a human duty of stewardship towards land and nature.
=== Culture ===
Many humans see land as a source of "spirituality, inspiration, and beauty." Many also derive a sense of belonging from land, especially if it also belonged to their ancestors. Various religions teach about a connection between humans and the land (such as veneration of Bhumi, a personification of the Earth in Hinduism, and the obligation to protect land as hima in Islam), and in almost every Indigenous group there are etiological stories about the land they live on. For Indigenous peoples, connection to the land is an important part of their identity and culture, and some religious groups consider a particular area of land to be sacred, such as the Holy Land in the Abrahamic religions.
Creation myths in many religions involve stories of the creation of the world by a supernatural deity or deities, including accounts wherein the land is separated from the oceans and the air. The Earth itself has often been personified as a deity, in particular a goddess. In many cultures, the mother goddess is also portrayed as a fertility deity. To the Aztecs, Earth was called Tonantzin—"our mother"; to the Incas, Earth was called Pachamama—"mother earth". In Norse mythology, the Earth giantess Jörð was the mother of Thor and the daughter of Annar. Ancient Egyptian mythology is different from that of other cultures because Earth (Geb) is male and the sky (Nut) is female.
Ancient Near Eastern cultures conceived of the world as a flat disk of land surrounded by ocean. The Pyramid Texts and Coffin Texts reveal that the ancient Egyptians believed Nun (the ocean) was a circular body surrounding nbwt (a term meaning "dry lands" or "islands"). The Hebrew Bible, drawing on other Near Eastern ideas, depicts the Earth as a flat disc floating on water, with another expanse of water above it. A similar model is found in the Homeric account of the 8th century BC in which "Okeanos, the personified body of water surrounding the circular surface of the Earth, is the begetter of all life and possibly of all gods."
The spherical form of the Earth was suggested by early Greek philosophers, a belief espoused by Pythagoras. Contrary to popular belief, most educated people in the Middle Ages did not believe the Earth was flat: this misconception is often called the "Myth of the Flat Earth". As evidenced by thinkers such as Thomas Aquinas, the European belief in a spherical Earth was widespread by this point in time. Prior to circumnavigation of the planet and the introduction of space flight, belief in a spherical Earth was based on observations of the secondary effects of the Earth's shape and parallels drawn with the shape of other planets.
=== Travel ===

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Humans have commonly traveled for business, pleasure, discovery, and adventure, all made easier in recent human history as a result of technologies like cars, trains, planes, and ships. Land navigation is an aspect of travel and refers to progressing through unfamiliar terrain using navigational tools like maps with references to terrain, a compass, or satellite navigation. Navigation on land is often facilitated by reference to landmarks – enduring and recognizable natural or artificial features that stand out from their nearby environment and are often visible from long distances. Natural landmarks can be characteristic features, such as mountains or plateaus, with examples including Table Mountain in South Africa, Mount Ararat in Turkey, the Grand Canyon in the United States, Uluru in Australia, and Mount Fuji in Japan.
Two major eras of exploration occurred in human history: one of divergence, and one of convergence. The former saw humans moving out of Africa, settling in new lands, and developing distinct cultures in relative isolation. Early explorers settled in Europe and Asia; 14,000 years ago, some crossed the Ice Age land bridge from Siberia to Alaska and moved southbound to settle in the Americas. For the most part, these cultures were ignorant of each other's existence. The second period, occurring over roughly the last 10,000 years, saw increased cross-cultural exchange through trade and exploration, marking a new era of cultural intermingling.
=== Trade ===
Human trade has occurred since the prehistoric era. Peter Watson dates the history of long-distance commerce from c. 150,000 years ago. Major trade routes throughout history have existed on land, such as the Silk Road which linked East Asia with Europe and the Amber Road which was used to transfer amber from Northern Europe to the Mediterranean Sea. The Dark Ages led trade to collapse in the West, but it continued to flourish among the kingdoms of Africa, the Middle East, India, China, and Southeast Asia. During the Middle Ages, Central Asia was the economic centre of the world, and luxury goods were commonly traded in Europe. Physical money (either barter or precious metals) was dangerous to carry over a long distance. To address this, a burgeoning banking industry enabled the shift to movable wealth or capital, making it far easier and safer to trade across long distances. After the Age of Sail, international trade mostly occurred along sea routes, notably to prevent intermediary countries from being able to control trade routes and the flow of goods.
In economics, land refers to a factor of production. It can be leased in exchange for rent, and use of its various raw material resources (trees, oil, metals).
=== Land use ===
Land is the foundation of agriculture, supporting over 95% of food production while providing essential ecosystem services that sustain life on Earth. As a finite resource, it faces pressures from competing demands including urban expansion, biofuel production, and changing consumption patterns driven by rising incomes and shifting diets. Land is the basis of food security, biodiversity conservation, climate regulation and in 2025 the livelihoods of 892 million agricultural workers worldwide.
For more than 10,000 years, humans have engaged in activities on land such as hunting, foraging, controlled burning, land clearing, and agriculture. Beginning with the Neolithic Revolution and the spread of agriculture around the world, human land use has significantly altered terrestrial ecosystems, with an essentially global transformation of Earth's landscape by 3000 years ago. From around 1750, human land use has increased at an accelerating rate due to the Industrial Revolution, which created a greater demand for natural resources and caused rapid population growth.
Agriculture includes both crop farming and animal husbandry. A third of Earth's land surface is used for agriculture, with estimated 16.7 million km2 (6.4 million sq mi) of cropland and 33.5 million km2 (12.9 million sq mi) of pastureland. This has had significant impacts on Earth's ecosystems. When land is cleared to make way for agriculture, native flora and fauna are replaced with newly introduced crops and livestock. Excessively high agricultural land use is driven by poor management practices (which lead to lower food yields, necessitating more land use), food demand, food waste, and diets high in meat.
Urbanization has led to greater population growth in urban areas in the last century. Although urban areas make up less than 3 percent of Earth's land area, the global population shifted from a majority living in rural areas to a majority living in urban areas in 2007. People living in urban areas depend on food produced in rural areas outside of their cities, which creates greater demand for agriculture and drives land use change well beyond city boundaries. Urbanization also displaces agricultural land because it mainly takes place on the most fertile land. Urban expansion in peri-urban areas fragments agricultural and natural lands, forcing agriculture to move to less fertile land elsewhere. Because this land is less fertile, more land is needed for the same output, which increases the total agricultural land use.
Another form of land use is mining, whereby minerals are extracted from the ground using a variety of methods. Evidence of mining activity dates back to around 3000 BCE in Ancient Egypt. Important minerals include iron ore, mined for use as a raw material; coal, mined for energy production; and gemstones, mined for use in jewellery and currency.
=== Law ===

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The phrase "the law of the land" first appeared in 1215 in Magna Carta, inspiring its later usage in the United States Constitution. The idea of common land also originated with medieval English law, and refers collective ownership of land, treating it as a common good. In environmental science, economics, and game theory, the tragedy of the commons refers to individuals' use of common spaces for their own gain, deteriorating the land overall by taking more than their fair share and not cooperating with others. The idea of common land suggests public ownership; but there is still some land that can be privatized as property for an individual, such as a landlord or king. In the developed world, land is expected to be privately owned by an individual with legal title, but in the developing world the right to use land is often divided, with the rights to land resources being given to different people at different times for the same area of land. Beginning in the late 20th century, the international community has begun to recognise Indigenous land rights in law, for example, the Treaty of Waitangi for Māori people, the Act on Greenland Self-Government for Inuit, and the Indigenous Peoples Rights Act in the Philippines.
=== Geopolitics ===
Borders are geographical boundaries imposed either by geographic features (oceans, mountain ranges, rivers) or by political entities (governments, states, or subnational entities). Political borders can be established through warfare, colonization, or mutual agreements between the political entities that reside in those areas; the creation of these agreements is called boundary delimitation.
Many wars and other conflicts have occurred in efforts by participants to expand the land under their control, or to assert control of a specific area of considered to hold strategic, historical, or cultural significance. The Mongol Empire of the 13th and 14th centuries became the largest contiguous land empire in history through war and conquest.
In the 19th-century United States, a concept of manifest destiny was developed by various groups, asserting that American settlers were destined to expand across North America. This concept was used to justify military action against the indigenous peoples of North America and of Mexico.
The aggression of Nazi Germany in World War II was motivated in part by the concept of Lebensraum ("living space"), which had first became a geopolitical goal of Imperial Germany in World War I (1914–1918) originally, as the core element of the Septemberprogramm of territorial expansion. The most extreme form of this ideology was supported by the Nazi Party (NSDAP). Lebensraum was one of the leading motivations Nazi Germany had in initiating World War II, and it would continue this policy until the end of World War II.
== Environmental issues ==
Land degradation is "the reduction or loss of the biological or economic productivity and complexity" of land as a result of human activity. Land degradation is driven by many different activities, including agriculture, urbanization, energy production, and mining. Humans have altered more than three-quarters of ice-free land through habitation and other use, fundamentally changing ecosystems. Human activity is a major factor in the Holocene extinction, and human-caused climate change is causing rising sea levels and ecosystem loss. Environmental scientists study land's ecosystems, natural resources, biosphere (fauna and flora), troposphere, and the impact of human activity on these. Their recommendations have led to international action to prevent biodiversity loss and desertification, and encourage sustainable forest and waste management. The conservation movement lobbies for the protection of endangered species and the protection of natural areas, such as parks. International frameworks have focused on analyzing how humans can meet their needs while using land more efficiently and preserving its natural resources, notably under the United Nations' Sustainable Development Goals framework.
=== Soil degradation ===
Human land use can cause soil to degrade, both in quality and in quantity. Soil degradation can be caused by agrochemicals (such as fertilizers, pesticides, and herbicides), infrastructure development, and mining among other activities. There are several different processes that lead to soil degradation. Physical processes, such as erosion, sealing, and crusting, lead to the structural breakdown of the soil. This means water cannot penetrate the soil surface, causing surface runoff. Chemical processes, such as salinization, acidification, and toxication, lead to chemical imbalances in the soil. Salinization in particular is detrimental, as it makes land less productive for agriculture and affects at least 20% of all irrigated lands. Deliberate disruption of soil in the form of tillage can also alter biological processes in the soil, which leads to excessive mineralization and the loss of nutrients.
Desertification is a type of land degradation in drylands in which fertile areas become increasingly arid as a result of natural processes or human activities, resulting in loss of biological productivity. This spread of arid areas can be influenced by a variety of human factors, such as deforestation, improper land management, overgrazing, anthropogenic climate change, and overexploitation of soil. Throughout geological history, desertification has occurred naturally, though in recent times it is greatly accelerated by human activity.
=== Pollution ===

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Ground pollution is soil contamination via pollutants, such as hazardous waste or litter. Ground pollution can be prevented by properly monitoring and disposing of waste, along with reducing unnecessary chemical and plastic use. Unfortunately, proper disposal of waste often is not economically beneficial or technologically viable, leading to short-term solutions of waste disposal that pollute the earth. Examples include dumping harmful industrial byproducts, overusing agricultural fertilizers and other chemicals, and poorly maintaining landfills. Some landfills can be thousands of acres in size, such as the Apex Regional landfill in Las Vegas.
Water pollution on land is the contamination of non-oceanic hydrological surface and underground water features such as lakes, ponds, rivers, streams, wetlands, aquifers, reservoirs, and groundwater as a result of human activities. It may be caused by toxic substances (e.g., oil, metals, plastics, pesticides, persistent organic pollutants, industrial waste products), stressful conditions (e.g., changes of pH, hypoxia or anoxia, increased temperatures, excessive turbidity, unpleasant taste or odor, and changes of salinity), or pathogenic organisms.
=== Biodiversity loss ===
The biodiversity of Earth—the variety and variability of life—is threatened by climate change, human activities, and invasive species. Due to an increase in the rate of extinction, biodiversity loss is increasing. Agriculture can cause biodiversity loss as land is converted for agricultural use at a very high rate, particularly in the tropics, which directly causes habitat loss. The use of pesticides and herbicides can also negatively impact the health of local species. Ecosystems can also be divided and degraded by infrastructure development outside of urban areas.
Biodiversity loss can sometimes be reversed through ecological restoration or ecological resilience, such as through the restoration of abandoned agricultural areas; however, it may also be permanent (e.g. through land loss). The planet's ecosystem is quite sensitive: occasionally, minor changes from a healthy equilibrium can have dramatic influence on a food web or food chain, up to and including the coextinction of that entire food chain. Biodiversity loss leads to reduced ecosystem services, and can eventually threaten food security. Earth is currently undergoing its sixth mass extinction (the Holocene extinction) as a result of human activities which push beyond the planetary boundaries. So far, this extinction has proven irreversible.
=== Resource depletion ===
Although humans have used land for its natural resources since ancient times, demand for resources such as timber, minerals, and energy has grown exponentially since the Industrial Revolution due to population growth. When a natural resource is depleted to the point of diminishing returns, it is considered the overexploitation of that resource. Some natural resources, such as timber, are considered renewable, because with sustainable practices they replenish to their previous levels. Fossil fuels such as coal are not considered renewable, as they take millions of years to form, with the current supply of coal expected to peak in the middle of the 21st century. Economic materialism, or consumerism, has influenced destructive patterns of modern resource usage, in contrast with pre-industrial usage.
== Gallery ==
Different varieties of landscapes:
== See also ==
Public land
Solid earth
== Notes ==
== Sources ==
This article incorporates text from a free content work. Licensed under CC BY 4.0 (license statement/permission). Text taken from The State of Food and Agriculture 2025​, Food and Agriculture Organization of the United Nations.
== References ==

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A landmark is a recognizable natural or artificial feature used for navigation, a feature that stands out from its near environment and is often visible from long distances.
In modern-day use, the term can also be applied to smaller structures or features that have become local or national symbols.
== Etymology ==
In Old English, the word landmearc (from land + mearc (mark)) was used to describe a boundary marker, an "object set up to mark the boundaries of a kingdom, estate, etc." Starting around 1560, this interpretation of "landmark" was replaced by a more general one. A landmark became a "conspicuous object in a landscape".
A landmark literally meant a geographic feature used by explorers and others to find their way back to their departure point, or through an area. For example, Table Mountain near Cape Town, South Africa, was used as a landmark to help sailors navigate around the southern tip of Africa during the Age of Exploration. Artificial structures are also sometimes built to assist sailors in navigation. The Lighthouse of Alexandria and the Colossus of Rhodes are ancient structures built to lead ships to the port.
In modern usage, a landmark includes anything that is easily recognizable, such as a monument, building, or other structure. In American English it is the main term used to designate places that might be of interest to tourists, due to notable physical features or historical significance. Landmarks in the British English sense are often used for casual navigation, such as giving directions. This is done in American English as well.
In urban studies as well as in geography, a landmark is furthermore defined as an external point of reference that helps orientation in a familiar or unfamiliar environment. Landmarks are often used in verbal route instructions ("Turn left at the big church and then right over the bridge.")
== Types ==
Landmarks are usually classified as either natural landmarks or human-made landmarks, both are originally used to support navigation on finding directions. A variant is a seamark or daymark, a structure usually built intentionally to aid sailors navigating featureless coasts.
=== Natural ===
Natural landmarks can be characteristic features, such as mountains or plateaus. Examples of natural landmarks are Mount Everest in the Himalayas, Table Mountain in South Africa, Mount Ararat in Turkey, Uluru in Australia, Mount Fuji in Japan and the Grand Canyon in the United States. Trees might also serve as local landmarks, such as jubilee oaks or conifers. Some landmark trees may be named, such as Queen's Oak, Hanging Oak and Centennial Tree.
Bases of fallen trees, known in this context as rootstocks, are used as navigational aids on high-resolution maps and in the sport of orienteering. Because most woods have many fallen trees, generally only very large rootstocks are mapped.
=== Human made ===
In the modern sense, landmarks are usually referred to as monuments or prominent distinctive buildings, used as the symbol of a certain area, city, or nation. Examples include:
Church spires and mosque minarets are often very tall and visible from many miles around and thus often serve as built landmarks. Also town hall towers and belfries often have a landmark character.
== See also ==
Boundary marker – Physical marker that identifies a land boundary
Contemporary history – Era from 1945–present
Cultural heritage management – Vocation and practice of managing cultural heritage
Daymark – Daytime aid to navigation
Heritage tourism – Tourism based on cultural heritage sites
National landmark (disambiguation)
National symbol – Symbol of a national community
== References ==
== External links ==

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