for Exploring GIS, by Nicholas Chrisman
Index to glossary entries (in alphabetic order)
A | B | C | D |
E | F | G | H |
I | J | K | L | M
| N | O | P | Q |
R | S | T | U |
The book has a running glossary with many terms defined at the
of the page. This resource collects all of those definitions and adds other
definitions that appear in the body of the text.
Page numbers refer to the printed version of the text.
These terms are © Copyright, 1997 John Wiley and Sons. Use of these
definitions should credit Exploring Geographic
Systems by Nicholas Chrisman.
- Absolute measurement p.16
- a level of measurement higher than
ratio where the unit of measurement
is not an arbitrary decision, so the numbers cannot be rescaled and retain
their meaning. Probability is an example of an absolute scale.
- Accuracy p. 27
- closeness of a measurement to a value thought to be true;
can be estimated by repeated measurement, measured by variance for
measures; accuracy of classification for categories can be summarized by
a misclassification matrix when compared to a survey of greater
- Areal interpolation p. 222
- transformation of an attribute of one set of choropleth zones to another
set of choropleth zones.
- Attribute p. 6
- the range of possible values of a characteristic; an attribute value
is a specific instance of the characteristic associated with a geographic
- axiom p. 24
- a proposition accepted as true without proof; an assumption that is
formally recognized. (component of data
- AVHRR p. 229
- Advanced Very High Resolution Radiometer, a satellite sensing
operated by the US National Oceanic and Atmospheric Administration
with a resolution of about 1.1 km, twice-daily repeat cycle, broad scenes
(2400 km), and four bands of spectral data.
Bézier curve p. 62
- a smooth curve that passes through specified points with a given
(tangent) at those points.
- bilinear interpolation p. 214
- interpolation method where the value is obtained by linear
on the two axes (row and column). Uses four neighbors from a raster
of the surface, and averages out the inconsistency between the four
- bit map p. 46
- a spatial data structure that records a binary value (presence or
absence of some attribute value) for a set of cells in a compact
- blunders p. 73
- errors, usually due to human operators, whose magnitude cannot be
modelled by regular statistical models.
- Boolean algebra p. 109
- system of operations applied to sets (and logical propositions);
variables are zero or one, hence strongly connected to modern computing;
originated by George Boole in 1847.
- breadth-first p. 200
- algorithms to traverse a tree that explore the structure by
each level totally before moving to a finer level; as opposed to
each path from the root to the 'leaves' (depth-first).
- buffer p. 142
- a zone constructed outwards from an isolated object to a specific
- CAD p. 31
- computer-aided design, software packages designed to automate
of mechanical drawings.
- cadastral p. 264
- pertaining to the legal register of land parcels, particularly for
land taxation or property transfer; more loosely, related to property
- cartographic scale p. 82
- formally, the ratio between distance measurements on a map and the
same distance on the ground (for example 1:24000). In a digital
this term refers to the complex (and often unwritten) rules for selection,
generalization and representation used for a
particular map series.
[Not to be confused with a scale of
- cartographic spaghetti p. 78
- a cartographic data structure that represents each feature as a
of coordinate pairs, and imposes no rules for relationships or logical
- case p. 24
- In statistics, an individual unit of observation. Selecting the unit
of analysis (discrete unit of control) establishes the measurement
for statistically based studies.
- categorical coverage p. 38
- an exhaustive partitioning of a two-dimensional region into
shaped zones that are defined by membership in a particular category of
a classification system.
- cell p. 44
- a regular unit of spatial sampling. Usually applied to area-based
measurement frameworks that treat a system of cells as an exhaustive
rather than a set of points. Often functionally identical to pixel.
- CGIS p. 71
- Canada Geographical Information System, perhaps the earliest,
one of the most ambitious, prototypes of a modern GIS. (Tomlinson 1967)
CGIS created a digital coverage of land suitability maps for the areas of
Canada with agricultural potential.
- chain p. 34
- a directed set of non-intersecting line segments with nodes at each
end and reference to left and right polygons.
- choropleth framework p. 52
- measurement framework
whose spatial units (derived from a categorical
coverage of named objects) serve as control
for attribute measurement
(e.g. census tabulation).
- choropleth map p. 13
- a thematic mapping technique that displays a quantitative attribute
using ordinal classes
applied as uniform symbolism over a whole areal feature.
Sometimes extended to include any thematic map based on symbolism
to areal objects.
- cluster analysis p. 203
- a procedure that groups points in a multidimensional space
measurements) into clusters that minimize the distance from cluster
(or some other objective function).
- Cohen's kappa p. 122
- a measure of agreement between two classifications. Defined as
accuracy - change agreement) / (1- chance agreement) where the chance
is estimated by the cross-product of marginal frequencies (statistical
- compression p. 67
- a software procedure that encodes a data structure so that its
occupies less space (under certain conditions); may preserve all the
(loss-less) or deliberately simplify.
- connected coverage frameworks p. 31
- a general term for measurement
frameworks that involve relationships
between distinct spatial objects; includes network
and categorical coverage
- contour p. 30
- a line connecting points of equal elevation on a topographic surface.
An control p. 27
- a mechanism of restraint on the variation of a system to permit
of one component of a phenomenon while other components only vary
the limits of the control.
- control point p. 72
- a feature whose location can be established in an external spatial
reference system (ideally, the Geodetic Reference System) and on the
material to be digitized.
- coordinates p. 18
- a structured set of measurements related to a specific spatial reference
system; usually applied to pairs of distance measurements (X,Y) on
axes of a planar reference system or to angular measurements such as
pairs on a spherical reference model.
- counts p. 16
- numerical measurements that aggregates the number of some
within a collection unit (for example population). Counts depend on the
definition of the objects counted, so they cannot be rescaled arbitrarily.
- course p. 161
- line on a surface where slopes converge from two directions. (See
Topology of Topography.)
- cubic convolution p. 214
- interpolation method where the value is interpolated by fitting a
third-order equation to the sixteen grid points surrounding the desired
- custodian p. 265
- an organization that takes responsibility to generate a particular
kind of information for a defined geographic region and agrees to make it
available to others.
- dasymetric p. 224
- a method proposed by John K. Wright to estimate densities using areal
interpolation and quantitative puzzle-solving; more generally, a type
thematic map whose boundaries are conditioned by some other
database p. 24
- structured collection of data with software to provide access in
ways; has a data model,
a data structure and an implementation (representation).
- database schema p. 245
- logical arrangement of tables, attributes, and integrity rules to
structure a database. Involves definitions of entities and their
- data dictionary p. 246
- detailed definitions of the codes employed for identifying objects
and for attribute values.
- data model p. 23
- In the database literature
1) general description of sets of entities and the relationships between
these sets of entities (Ullman 1982)
2) collection of object types, collection of operators on those object
and a collection of integrity constraints (Codd 1981).
[Integrity constaints are the axioms of a data
In a GIS, composed of a measurement framework
and a scheme for representation.
- data structure p. 57
- arrangement of data entities that permits the construction of
through software operations; implements a data
- Delaunay triangulation p. 153
- a network that connects each point in a set of points to its nearest
neighbors; topological 'dual' of
the Voronoi network.
- DEM p. 41
- a framework for recording spot elevations in a regular rectangular
grid (matrix); an acronym originally created from Digital Elevation Model
at US Geological Survey. To avoid ambiguity, DEM will be used exclusively
for a grid framework, so it can be read matrix.
- derived measurement p. 8
- numerical measurements constructed from the relationship of other
measurements (for example, a density is a ratio of weight by volume).
[As opposed to extensive measurements.]
- diagonal p. 121
- cells in a square matrix whose row and column indices are the same.
In a transition matrix, they represent no change; in an error matrix they
represent no error.
- Digital Line Graph (DLG) p. 82
- a data format developed by US Geological Survey National Mapping
that uses a topological vector model.
- digitizer p. 70
- a manually controlled machine that records a spatial measurement
on the surface of a tablet.
- DIME p. 86
- Dual Independent Map Encoding, a digital database of streets and
census boundaries developed to conduct the 1970 US Decennial Census; an
early and prominent implementation of a topological data structure.
- discount rate p. 240
- economic factor that deflates a future sum to make it comparable
current expenses. Reflects expectations of interest rates and inflation.
- dynamic segmentation p. 55
- a method for referencing attribute information along a network that
does not divide each segment of the network wherever any attribute
- easement p. 236
- a legal agreement that grants partial rights over a portion of a
such as a utility easement to install overhead wires or underground pipes.
Also applied to rights-of-way for roads.
- efficiency p. 235
- compares the resources expended to attain a given product
- effectiveness p. 235
- compares the nature of the products and the process of creating
- ellipsoid p. 60
- three dimensional object formed by rotating an ellipse around its
minor axis; an oblate ellipsoid approximates the shape of the Earth (geoid),
computed by the best fit to geodetic observations. See Table 3-2 p. 76
- equal interval p.93
- a classification procedure that divides the total range of attribute
values by the number of classes; breakpoints are spaced at equal
whether the class has any member or not.
- extensive measurement p. 8
- numerical measurements along an axis where addition provides the
rule; the base units of SI are extensive, as are units of
(dollars, pounds sterling, francs, euros).
- feature p. 31
- cartographic feature: an instance of a defined class of objects that
cannot be divided into objects of the same type. 31
- field p. 29
- an abstract construct of a mathematical relationship viewed as a
structure. In physics: a region of space subject to a force (as a magnetic
field). In GIS, often used as a synonym for surface.
- flexible production p. 257
- a system of economic organization characterized by rapid changes in
production plans, "just in time" delivery, and other techniques
that break from the economy of scale, mass production approach
by the assembly line.
- foreign key p. 97
- item in a relational table that contains a value identifying rows
in another table; represents a relationship between two elements of a relational
- fuzzy set theory p. 16
- an extension to set theory that permits an object to have a degree
of membership (usually represented as a number between zero and one).
membership values do not have to follow the rules of probability.
- fuzzy tolerance p. 114
- a distance within which intersections and points will be treated as
coincident. To be processed correctly, the fuzzy tolerance cannot be
immediately (otherwise a point might be moved twice and beyond its
tolerance). A 'cluster' of points must be grouped so that no point is moved
more than the tolerance.
- generalization p. 83
- In cartography, conversion of a geographic representation to one
less resolution and less information content; traditionally associated
a change in scale.
- geodetic p. 76
- related to the science of earth measurement (geodesy).
- geodetic control p. 29
- a set of surveyed monuments used to define a spatial reference system
for a particular project.
- geoid p. 6
- three-dimensional shape of the Earth defined by the surface where
gravity has the value associated with Mean Sea Level.
[The geoid is lumpy, while an ellipsoid is
representing the average elevation of the geoid to some level of
- geographic information system (GIS) p. 5
- 1) "a system of hardware, software, data, people,
and institutional arrangements for collecting, storing, analyzing and
information about areas of the earth." (Dueker and Kjerne, 1989, p.
[Commentary on this accepted definition]
- 2) the organized activity by which people measure aspects of
phenomena and processes; represent these measurements, usually in the
of a computer database, to emphasize spatial themes, entities and
operate upon these representations to produce more measurements and to
new relationships by integrating disparate sources; and transform these
representations to conform to other frameworks of entities and
These activities reflect the larger context (institutions and cultures)
in which these people carry out their work. In turn, the GIS may influence
these structures. [This definition in more graphic
- geostatistics p. 181
- branch of statistical estimation concentrating on the incorporation
of spatial measures, particularly distance and neighborhood, into models.
- GIRAS p. 155
- Geographic Information Retrieval and Analysis System, a project
by US Geological Survey in the 1970s; produced vector interpretations of
land use/land cover stored in an early topological data structure.
- GPS p. 77
- Global Positioning System, a constellation of communications
that broadcast timing signals that can be converted into a distance
permitting trilateration (surveying by knowing the sides of triangles).
- graphic elements p. 15
- the characteristics of a symbol system that can be manipulated to
encode information (also called 'visual variables', graphic dimensions,
etc.). For cartography, these include size, shape, hue, saturation,
orientation and pattern. (See Robinson and others, 1995).
- ground truth p. 121
- a determination of geographic attributes judged to be of higher
usually applied to a 'point' classified into a land use/land cover category.
- 'heads-up' digitizing p. 71
- a digitizing station that provides a graphical user interface on the
screen of a workstation (hence sometimes called on-screen digitizing).
operator uses a pointing device (mouse or trackball) to navigate on the
scanned image of the original source, without having to look down at a
- heuristic p. 201
- a procedure that attacks a problem in a way directed towards the
but not guaranteed to attain it exactly.
- indirect measurement p. 50
- a procedure that assigns attributes to spatial objects through some
attribute of those spatial objects (such as a soil class or a political
subdivision), not through direct measurement.
- information p. 8
- data (observations, measurements, etc.) placed in context of a
of meaning (a set of relationships and assumptions about those
Information, built into larger context, constructs knowledge. [Loosely
as a difference that makes a difference.]
- integrated survey p. 137
- an approach to land evaluation that combines the opinions of many
disciplines in producing a common representation of the processes that
- interval p. 12
- a level of measurement
that assigns numerical values to objects, but
does not provide a 'zero' value to serve as a reference. Differences
interval values have meaning as ratio measures.
- invariance p. 10
- properties that remain unchanged despite transformations of the
used to represent a measurement.
- isolated object frameworks p. 30
- a general term covering those measurement
that use a specific
attribute value as a control to obtain spatial
object and isoline frameworks.
- isoline p. 30
- a line connecting points of equal elevation on a surface (See contour)
- isoline framework p. 30
- a measurement framework that establishes
control by a systematic set
of slices through an attribute to obtain lines that represent the surface.
- join p. 97
- procedure that attaches values from a database table to another
based on matching a foreign key to its primary
- kriging p. 212
- a geostatistical technique for interpolation
that uses information
about the spatial autocorrelation in the vicinity of each point to provide
'optimal' interpolation (in the sense of greater use of the information
provided by the spatial arrangement).
- Landsat p. 29
- a series of Earth-observing satellites. The early ones (first launched
in 1972) had 80m resolution; the more recent ones include the 30m TM sensor.
- land system p. 247
- a unit of an integrated survey where
common processes (involving soils,
vegetation and other factors) have created a combination of features that
will support a particular group of uses.
- layer p. 18
- a collection of related geographic data. Depending on context, a layer
may have some specific relationship to other layers. For raster imagery,
a layer can represent one sensor in a multispectral array. In some cases,
a layer may contain a coverage, hence provide an attribute value at all
locations. In some cases, a layer simply collects all features with a
- least-squares p. 73
- an estimation procedure that minimizes the sum of squared
between observations and a numerical model for those observations; used
in ordinary regression analysis and many other statistical procedures.
- level of measurement p. 9
- a grouping of measurement scales based on the invariance of certain
properties. Measurement scales
at a common level of measurement can be transformed
into another scale at the same level without reducing the information
- LLRW p. 126
- Low Level Radioactive Waste; Low-level waste is generated (on the
order of 160,000 m3 for the US per year) by nuclear power plants,
and various other industries; excludes waste from weapons construction
the spent fuel from nuclear reactors (high-level waste).
- mandates p. 265
- organizing principles of purpose that drive an organization; in a
bureaucracy, the laws, administrative rules and regulations that define
the purpose and content of actions.
- measurement framework p. 23
- a scheme that establishes rules for control
of other components of
a phenomenon that permit the measurement of one component. In a
information system, there are three components: time, space,
- information describing a collection of data; includes source, access
issues, format, schema and data quality.
- national grid p. 74
- a spatial reference system usually adopted
by legal or administrative
procedures for use through a given country. Typically consists of a projection
or a system of projection zones plus a geodetic
- NDVI p. 220
- difference between two bands (near infrared minus visible red)
by the sum of the two bands; high values indicate active vegetation
often applied to NOAA AVHRR data.
- network framework p. 35
- a measurement framework based on a set
of distinct spatial objects (usually instances of linear objects like roads
or rivers) that connect to form a network.
- node p. 34
- a zero-dimensional object that is a topological junction (or end
and a geometric location. (Definitions for topological objects simplified
- nominal p. 10
- a level of measurement based assigning
objects into discrete categories.
- North American Datum p. 76
- an adjustment of geodetic measurements
that provides the horizontal reference for North America. The 1927 Datum
held Mead's Ranch, Kansas as a fixed point, while the 1983 Datum
a simultaneous adjustment of all measurements. 1927 uses the Clarke's
while 1983 uses the 1980 Geodetic Reference System. The plural of a
datum is 'datums', despite the Latin origins.
- NP-Complete p. 203
- class of algorithms conjectured to exhibit worst case performance
that cannot be written as a polynomial equation of the number of objects
- objective function p. 201
- the formula giving the goal in an optimization problem.
- ordinal p. 10
- a level of measurement that orders objects
or categories, but does
not provide further information regarding the distance between items.
- parcel p. 226
- contiguous unit of the earth's surface defined by a common
of legal rights.
- peak p. 161
- point of local divergence on a surface; all neighboring points are
lower. (Topology of topography)
- pixel p. 29
- smallest resolvable unit in an image; an area (usually rectangular)
forming a part of a systematic, uniform division of a study area.
of picture element.
- planar graph p. 37
- an arrangement of nodes and lines such that the lines intersect only
at nodes, thus remaining embedded in a plane (or a surface topologically
transformable onto a plane).
- point-in-polygon p. 116
- procedure to determine which points fall into which polygons; can
attach attributes to either the points or the polygons.
- polygon p. 34
- an area (bounded continuous two-dimensional object) consisting of
an interior area, one outer ring and zero or more non-
- polygon overlay p. 108
- a procedure that calculates the geometric relationships between
geographic representations (usually applied to vector models); used to
attribute information .
- primitives p. 31
- basic components that are sufficient to build a larger system; the
primitives of two-dimensional geometry are points, lines, and areas.
- projection p. 60
- coordinate transformation that converts latitude longitude
into planar coordinates. Projections can be based on a developable surface
(such as a plane, cylinder, or cone) or on a mathematical function.
- proportional symbols p. 13
- a thematic mapping technique that displays a quantitative attribute
by varying the size of a symbol. Typically, proportional symbols use
shapes such as circles, and are scaled so that the area of the symbol is
proportional to the attribute value. Proportional symbols are located at
a point, even when they represent information collected for an area.
- prototype p. 16
- an approach to categorization that defines a category by identifying
a particular object as the typical example. Other objects assigned to this
category may not not share all characteristics with the prototype object.
The degree of resemblance can be treated as a distance in a taxonomic
- quadtree p. 67
- a spatial data structure that organizes a hierarchical structure of
square cells through iterative division into four daughter cells (Samet
- quantile p. 93
- a classification procedure that assigns an equal number of objects
into each class. The interval of each class will vary unless the
is completely uniform.
- raster p. 65
- a spatial data model based upon a regular tessellation of a surface
into pixels or grid cells.
- ratio p. 12
- a level of measurement
that includes both extensive
and derived measurements.
The numerical values of the measurement have a meaningful zero
and a fixed unit of measure.
- ray-casting p. 187
- computational technique used to simulate a visual scene with
effects, variations in light sources and other effects; usually developed
for arbitrary 3D objects, not just a single surface.
- recursive p. 83
- a programming procedure that invokes itself to subdivide a problem.
- registration p. 72
- the process of connecting a spatial representation to a broader spatial
- relational database p. 97
- a data model based on set theory.
Each set has elements that can be
uniquely defined by a primary key. A table (relation) stores all records
for a set. Each record in a table has the same columns for attribute values.
Relationships between tables are constructed by storing the key to a
in the other table (a foreign key).
- representation p. 57
- a symbolic mechanism to encode data. Using computers, involves a
model, a data structure and its implementation.
- representationalism p. 9
- a philosophy of measurement that defines measurement as the
of numbers with entities which are not numbers. The numbers are not seen
as inherent but as a representation of a defined aspect of the entity. [This
philosophy is opposed to the classical theory that measurement is the
expression of one quantity relative to another; quantities were seen as
- resampling p. 214
- a transformation usually applied to convert raster data into another
arrangement of raster cells. May require interpolation to determine the
attribute at a position not sampled by the original grid.
- resolution p. 27
- least detectable difference in a measurement; in a geographic
resolution applies to all components (time, space and attribute) according
to the measurement framework.
Not identical to accuracy.
- retraced line p. 63
- a technique applied to simple vector data structures to embed inner
rings within outer rings. A line that is repeated (drawn twice) should not
- ridge p. 161
- line along which a surface diverges in two different directions. (Topology
- ring p. 35
- a sequence of non-intersecting chains that close.
- scalar field p. 158
- a surface whose value can be represented
by a single number.
- scale (measurement) p. 10
- a system used to encode the results of a measurement; typically a
number line, but generalized to include a list of categories. [Distinct
from cartographic scale.]
- setback p. 142
- a zone inside a polygon constructed by a fixed distance from the
of the polygon; typically used to restrict building or activities too close
to the edge of a property parcel.
- SI p. 9
- Système International d'Unités; the system of
and measures established by international agreement in 1875. The
Bureau of Weights and Measures in Sèvres, France oversees the
standards. SI defines seven base units from which many others can be
meter-length, kilogram-mass, second-time, kelvin-temperature, ampere-
current, mole-chemical quantity, candela- intensity of light.
- sliver p. 114
- an artifact of polygon overlay; usually
created by overlay of two
sources with different accuracy, different sources or different
- slope p. 158
- a multicomponent property associated with a surface at each point;
the vertical component (gradient) expresses the local rate of change, the
horizontal component (aspect) gives the direction.
- soil inclusions p. 52
- a category of soil expected to occur inside the units mapped as
- spatial autocorrelation p. 181
- degree of correlation between a surface value and the values of its
neighbors; propensity of spatial data to vary smoothly.
(Core element of geostatistics.)
- Spatial Data Transfer Standard (SDTS) p. 34
- a specification of generic data formats and metadata content to
interchange of geographic information. Adopted by the US Government as
Information Processing Standard (FIPS) 173.
- spatial object framework p. 30
- a measurement framework
that identifies a particular category, then
maps the location of that object (as a point, a line or an area).
- spatial reference system p. 18
- a mechanism to situate measurements on a geometric body, such as
Earth; establishes a point of origin, orientation of reference axes, and
geometric meaning of measurements, as well as units of
[basis of coordinates.]
- spline p. 62
- a smooth curve that models the behavior of a thin spring (with a
modulus of elasticity) constrained to pass through specified points.
- SQL p. 93
- Structured Query Language; a standard interface for access to a relational
database through queries that select records matching logical
- stand p. 237
- a contiguous area of a forest considered to be homogeneous in its
ability to support the intended forest crop. Used to direct forest practices
such as planting, thinning, and harvest.
- surface p. 29
- a spatial distribution which associates a single value with each
in a plane; (technically a field of a single-valued function) usually
with continuous attributes.
- SYMAP p. 211
- SYnagraphic MAPping package, developed under the direction of
Fisher at Harvard Laboratory for Computer Graphics beginning in 1966.
- temporal reference system p. 17
- an agreed measurement scheme for time; involves a time to start
(an origin) and a unit. International conventions establish a calendar and
synchronized clocks based on Greenwich Mean Time.
- tensor p. 158
- a multi-component surface of higher degree than a vector. The
of relativity requires tensors to handle space-time and electromagnetic
- TIFF p. 67
- Tagged Image File Format: a family of image encoding formats which
can vary the resolution and the number of bits used to represent each cell.
- TIN p. 49
- Triangulated Irregular Network: a system of terrain representation
that builds triangular facets to connect point heights. The points and
are chosen to represent a surface within some limits.
- TM p. 230
- Thematic Mapper, a satellite sensing system with resolution of 30
meters, 16 day repeat cycle, 185 km scene width and seven bands of
data; launched by NASA.
- topology p. 34
- a branch of mathematics concerned with those properties of
which are independent of a distance metric and are unchanged by any
deformation. In cartography, topology refers to combinatorial topology.
The other branch, point-set or algebraic topology, "emerged in the
twentieth century as a subject that unifies almost the whole of
(Boyer and Merzbach 1991, p. 622) and is used as the basis for relational
- topology of topography p. 161
- qualitative (ordinal) relationships in the structure of a surface.
Topography refers to the surface of the earth.
- transverse p. 75
- a projection oriented at right angles to
the equator. A transverse
cylindric projection uses a meridian of longitude as its central meridian.
- travelling salesman problem p. 203
- given a graph connecting a set of nodes, devise a route that visits
each node in the graph exactly once and minimizes the total cost
- trend surface p. 210
- result of a statistical fit of the observed values using a selected
spatial equation (from a plane up to higher order shapes).
- unit of measure p. 94
- the reference value used to establish a ratio-scaled measure;
the value of 1 for a ratio scale.
- USLE p. 137
- Universal Soil Loss Equation; predicts average soil loss (in tons)
for a period of time (a storm event or a year) as the product of six factors:
Rainfall intensity, Erodability of the soil, Length of slope, Slope gradient,
Crop, and Practices.
- UTM p. 75
- Universal Transverse Mercator; a spatial
reference system using a
set of transverse Mercator
projections six degrees wide that cover the
(except for polar regions covered by two Polar Stereographic projections).
- variable length list p. 59
- a data structure that can store a flexible number of elements in an
ordered sequence. Frequently implemented with a count followed by the
of the list.
- vector p. 62
- a spatial data model based on geometric primitives (point, line, and
area), located by coordinate measurements in a spatial reference system;
from mathematical term for a direction, or a directed line segment.
- vector field p. 158
- a multi-component surface whose values have a quantity and a
in space. Newtonian physics can be expressed as vectors. This
term is the origin of the term 'vector' applied
to a geometric data structure, but the connection is indirect.
- Voronoi network p. 153
- a set of lines that divides a plane into the area closest to each
of a set of points. The lines are perpendicular bisectors of the lines
nearest points (Delaunay triangulation).
- watershed p. 161
- area bounded by ridges that would converge (downhill) to a single
exit point. (see topology of topography)
- well-defined point p. 76
- a point-like (isolated) feature that can be distinguished on the
and on the ground to sufficient accuracy;
in US National Map Accuracy Standards
of 1947, implemented as 'plottable to .01 inch'.
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