GIS Definitions: A-D
Definitions of some commonly used GIS (Geographic Information System) terms.
A B C
D Full glossary:
- Arc attribute table. A
table containing attributes for arc coverage features. In addition
to user-defined attributes, the AAT contains the from and to nodes,
the left and right polygons, the length, an internal sequence number
and a feature identifier. See also feature
- ACCESS directory
- The system directory that
LIBRARIAN uses to store the files that manage access to the library.
Each library has an ACCESS directory located in the library's DATABASE
- An aggregate measure of
how reachable locations are from a given location. The ACCESSIBILITY
command computes values for accessibility as a function of the distance
between locations and an empirically derived distance decay parameter.
- The privileges accorded
a user for reading, writing, deleting, updating and executing files
on a disk. Access rights are stated as 'no access', 'read only' and
- ACODE file
- An INFO data file storing
arc attributes for coverages created from TIGER, DIME, IGDS and Etak
files. ACODE stands for 'Arc CODE'. The ACODE file is related by Cover-ID
to the Arc Attribute Table (AAT) of the coverage.
- address matching
- A mechanism for relating
two files using address as the relate item. Geographic coordinates
and attributes can be transferred from one address to the other. For
example, a data file containing student addresses can be matched to
a street coverage that contains addresses creating a point coverage
of where the students live.
- 1. Arc Digitizing System.
A simple digitizing and editing system used to add arcs and label
points to a coverage.
2. A command at the Arc: prompt that starts an ADS session.
- The process of assigning
arcs in a network to the closest center until the maximum impedance
or resource capacity of the center is reached.
- ARC Macro Language. A
high-level algorithmic language for generating end-user applications.
Features include the ability to create on-screen menus, use and assign
variables, control statement execution, and get and use map or page
unit coordinates. AML includes an extensive set of commands that can
be used interactively or in AML programs (macros) as well as commands
that report on the status of ArcInfo environment settings.
- Analysis is the process
of identifying a question or issue to be addressed, modeling the issue,
investigating model results, interpreting the results, and possibly
making a recommendation. See model
- 1. Descriptive text used
to label coverage features. It is used for display, not for analysis.
2. One of the feature classes in a coverage used to label other features.
Information stored for annotation includes a text string, the location
at which it is displayed, and a text symbol (color, font, size, etc.)
for display. See also TAT.
- American National Standards
Institute is a national coordinator of voluntary standards activities,
and an approval organization and clearinghouse for consensus standards
in the United States. ANSI works closely with international organizations,
particularly ISO, for
the development and approval of international standards. While ANSI
standards apply to every facet of today's world, their efforts in
the area of SQL and spatial extensions to SQL are of particular interest
to the GIS community.
- Application program interface
(API). An API is a set of system calls or routines for application
programs to access services from operating systems or other programs.
An API allows your program to work with other programs, possibly on
other computers. API is fundamental to client/server computing. ArcView
provides this service to ArcInfo users.
- 1. An ordered string of
vertices (x,y coordinate pairs) that begin at one location and end
at another. Connecting the arc's vertices creates a line. The vertices
at each endpoint of an arc are called nodes.
2. A coverage feature class used to represent linear features and
polygon boundaries. One line feature can contain many arcs. Arcs are
topologically linked to nodes (arc-node
topology) and to polygons (polygon-arc
topology). The descriptive attributes of arcs are stored in the
arc attribute table (AAT). See also node.
- The topological data structure
ArcInfo uses to represent connectivity between arcs and nodes. Arc-node
topology supports the definition of linear feature and polygon boundaries,
and supports analysis functions such as network tracing. See also
- A preserved collection
of historical information purged from an ArcStorm database.
- ArcStorm (ArcStorageManager)
is a data storage facility and transaction manager for ArcInfo data.
ArcStorm manages a feature-oriented database that can be closely integrated
with database systems supported by ArcInfo's DATABASE
- An ArcStorm database is
a collection of libraries, layers, INFO tables and external DBMS tables.
Data stored in an ArcStorm database benefit from the transaction management
and data archiving capabilities of ArcStorm.
- ArcTools is a collection
of ArcInfo productivity tools implemented through an AML-based
(ARC Macro Language) graphical
user interface. ArcTools provides a user-friendly approach to
commonly used ArcInfo operations and functions.
- 1. A homogeneous extent
of the Earth bounded by one or more arc features (polygon)
or represented as a set of polygons (region).
Examples: states, counties, lakes, land-use areas, and census tracts.
2. The size of a geographic feature measured in unit squares. ArcInfo
stores an area measure for each polygon and region.
- American Standard Code
for Information Interchange. A set of codes for representing alphanumeric
information (e.g., a byte with a value of 77 represents a capital
M). Text files, such as those created with the text editor of a computer
system, are often referred to as ASCII files.
- The compass direction
toward which a slope faces, measured in degrees from North in a clockwise
- ARC Standard Raster Graphic.
Raster graphic data transformed to the Equal ARC-second Raster Chart/Map
(ARC) Projection System. See SRG.
ASRG (using RGB) is very similar to DMA (Defense Mapping Agency) ADRG
(ARC Digitized Raster Graphic). ADRG files can be imported into ArcInfo
with the ADRGGRID command. The ASRG (using RGB) can be converted with
the ADRGGRID command if it is in a true DMA ADRG format. The ASRG
permits color codes, which the ADRGGRID command does not handle.
- The property or properties
of a location that create an incentive for trips to be made to that
location. For example, the attractiveness of a retail store could
be a function of the retail floor space, number of parking spaces,
product pricing, or a combination of these factors.
- 1. A characteristic of
a geographic feature described by numbers, characters, images and
CAD drawings, typically stored in tabular format and linked to the
feature by a user-assigned identifier (e.g., the attributes of a well
might include depth and gallons per minute).
2. A column in a database table. See also item.
- An INFO or other tabular
file containing rows and columns. In ArcInfo, attribute tables are
associated with a class of geographic features, such as wells or roads.
Each row represents a geographic feature. Each column represents one
attribute of a feature, with the same column representing the same
attribute in each row. See also feature
- The horizontal direction
of a vector, measured clockwise in degrees of rotation from the positive
y-axis, for example, degrees on a compass.
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- A copy of a file, a set
of files, or whole disk for safekeeping in case the original is lost
- One layer of a multispectral
image representing data values for a specific range of the electromagnetic
spectrum of reflected light or heat (e.g., ultraviolet, blue, green,
red, near-infrared, infrared, thermal, radar, etc.). Also, other user-specified
values derived by manipulation of original image bands. A standard
color display of a multispectral image shows three bands, one each
for red, green and blue. Satellite imagery such as LANDSAT TM and
SPOT provide multispectral images of the Earth, some containing seven
or more bands.
- band separate
- An image format that stores
each band of data collected by multispectral satellite scanning instruments
in a separate file.
- A measure of the volume
of data that can flow through a communications link. Image data tend
to exist as large data sets; thus moving image data sets from one
computer to another requires high bandwidth or performance will be
slowed. Also known as throughput.
- A map containing geographic
features used for locational reference. Roads, for example, are commonly
found on basemaps.
- base table
- A table that is physically
stored in the database. Compare with view.
- baud rate
- A measure of the speed
of data transmission between computer and other devices, measured
in bits per second.
- The smallest unit of information
that a computer can store and process. A bit has two possible values,
0 or 1, which can be interpreted as YES/NO, TRUE/FALSE, or ON/OFF.
See also byte.
- Binary large object. The
data type of a column in an RDBMS table which can store large image
or textual data as attributes.
- The file in a coverage
or grid which contains the coverage
- A type of expression that
reduces to a true or false (logical) condition. A Boolean expression
contains logical expressions (e.g., DEPTH > 100) and Boolean operators.
A Boolean operator is a keyword that specifies how to combine simple
logical expressions into complex expressions. Boolean operators negate
a predicate (NOT), specify a combination of predicates (AND), or specify
a list of alternative predicates (OR). For example, DEPTH > 100
AND DIAMETER > 20. See also logical
- border arcs
- 1. The arcs that create
the outer edge boundary of a polygon coverage.
2. In LIBRARIAN, the tile boundary arcs that split a polygon coverage
- A linear feature that
defines and controls the surface behavior of a tin
in terms of smoothness and continuity. Breaklines are always maintained
as linear features in a tin. Stereo-digitized features containing
x,y,z values such as streams and shorelines containing an elevation
attribute are often stored as breakline features.
- A zone of a specified
distance around coverage features. Both constant- and variable-width
buffers can be generated for a set of coverage features based on each
feature's attribute values. The resulting buffer zones form polygons-areas
that are either inside or outside the specified buffer distance from
each feature. Buffers are useful for proximity analysis (e.g., find
all stream segments within 300 feet of a proposed logging area).
- An error in a computer
program or in a piece of electronics that causes it to malfunction.
- A memory and data storage
unit composed of contiguous bits,
usually eight. For example, file sizes are measured in bytes or megabytes
(one million bytes). Bytes contain values of 0 to 255 and most often
represent integer numbers or ASCII characters (e.g., a byte with an
ASCII value of 77 represents
a capital M). A collection of bytes (often 4 or 8 bytes) represents
real numbers and integers larger than 255.
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- Computer-aided design.
An automated system for the design, drafting, and display of graphically
- CAD drawing
- The digital equivalent
of a drawing, figure or schematic created using a CAD system. For
example, a drawing file or DWG file in AutoCAD.
- The process of choosing
attribute values and computational parameters so that a model properly
represents the real-world situation being analyzed. For example, in
pathfinding and allocation, calibration generally refers to assigning
or calculating appropriate values to be entered in impedance and demand
- The maximum resource that
can be assigned (allocated) to or be serviced by a center.
For example, the capacity of a school is the number of students that
can be enrolled there.
Cartesian coordinate system
- A two-dimensional, planar
coordinate system in which x measures horizontal distance and y measures
vertical distance. Each point on the plane is defined by an x,y coordinate.
Relative measures of distance, area, and direction are constant throughout
the Cartesian coordinate plane.
- Computer-Aided Software
Engineering. CASE tools are defined programming rules for applying
engineering principles, methods, techniques, and concepts. These tools
assist in accomplishing a definable engineering task in the software
design process by automating manual activities through structured
prototyping. This technique reduces customized development time, supplying
consistent code sets and supporting the entire software life cycle
- Comité Consultatif
Internationale de Télégraphique et Téléphonique
(Consultative Committee on International Telephone and Telegraph).
CCITT is a technical committee of the International Telecommunications
Union, a United Nations organization in Geneva. It sets international
communications recommendations concerning standardization of data
interfaces, modems, and data networks. ArcInfo is fully compliant
with CCITT Group IV, the Standard for raster data compression. ArcInfo
supports the following TIFF
compression schemes: CCITT Group 4 for black-and-white data (read
only); CCITT Group 3, one-dimensional encoding for black-and-white
data; and PackBits.
- Compact Disk-Read Only
Memory. CD-ROM is an optical media. A CD-ROM 5.25-inch disk can hold
about 650 megabytes of information. The ISO 9660 standard defines
the format of data held on CD-ROM.
- See grid
- A discrete location that
has a supply of a resource or commodity. In spatial interaction, a
center is consider to have attractiveness.
- Computer Graphics Metafile
is a graphic image exchange standard, ANSI: x3.122-1986, ISO: 8632-1986,
for graphic output file format. ArcInfo, ArcView Version 2, and PC
ARC/INFO support CGM.
- 1. A letter (e.g., a,
b, c, or d), digit (e.g., 1, 2, or 3), or special graphic symbol (e.g.,
*, |, or -) treated as a single unit of data.
2. A data type for an attribute designating that values for the attribute
will be represented using characters. For example, the character data
type would be appropriate for the attribute COUNTRY, if the values
assigned are like United States, Brazil, Canada, Thailand, and so
- Checkin is the act of
returning ArcStorm data which was previously checked out for update
purposes. When modified data is checked in, all locks on the data
- Checkout is the act of
taking selected data out of an ArcStorm database into a local coverage
for editing purposes. When data is checked out, it is locked to prevent
updates from other users. ArcStorm data cannot be modified directly,
it must first be checked out.
- A software system is said
to have a client/server architecture when there is a central process
(server) which accepts requests from multiple user processes (clients).
ArcStorm is one example of a client/server architecture within ArcInfo.
- The spatial extraction
of those features from one coverage that reside entirely within a
boundary defined by features in another coverage (called the clip
coverage)-clipping works much like a cookie cutter.
- 1. Abbreviation of the
term COordinate GeOmetry. Land surveyors use COGO functions to enter
survey data, to calculate precise locations and boundaries, to define
curves, and so on.
2. The name of the ArcInfo coordinate geometry software product.
- The vertical dimension
of a table. A column has a name and a data type applied to all values
in the column.
- A specific instruction
to a computer program, issued by the user to perform a desired action.
command line interface
- A software product that
allows the user to type in commands at a prompt. Contrast to forms
- To make permanent any
changes made during a database transaction. Compare with roll
- concurrency management
- A database management
process for maintaining consistency of the data while supporting simultaneous
access by more than one user. A typical technique is to allow any
number of users read access but to allow only one user to have write
access. A second user wanting write access will have to wait until
the first person completes their transaction.
- conditional operator
- A symbol or keyword specifying
how to compare values. Conditional operators are used to query a database.
Examples from SQL include:
= (equal to) BETWEEN
< (LESS THAN) LIKE
> (greater than) CONTAINING
- A set of functions and
procedures that aligns the arcs of one coverage with those of another
and then transfers the attributes of one to the other. Alignment precedes
the transfer of attributes and is most commonly performed by rubber-sheeting
- The topological identification
of connected arcs by recording the from- and to-node for each arc.
Arcs that share a common node are connected. See also arc-node
- Limits imposed on a model.
For example, in an interaction model, specifying that the number of
trips generated from an origin to all destinations cannot exceed the
origin's production capacity.
- The topological identification
of adjacent polygons by recording the left and right polygons of each
arc. See also polygon-arc
- continuous data
- A surface for which each
location has a specified or derivable value. Typically represented
by a tin or lattice (e.g., surface elevation).
- A line connecting points
of equal surface value.
- contour interval
- The difference in surface
values between contours.
- A set of numbers that
designate location in a given reference system, such as x,y in a planar
coordinate system or an x,y,z in a three-dimensional coordinate system.
Coordinates represent locations on the Earth's surface relative to
other locations. See also vector
and Cartesian coordinate system.
- coordinate geometry
- See COGO.
- A reference system used
to measure horizontal and vertical distances on a planimetric map.
A coordinate system is usually defined by a map projection, a spheroid
of reference, a datum, one or more standard parallels, a central meridian,
and possible shifts in the x- and y-directions to locate x,y positions
of point, line, and area features.
In ArcInfo, a system with units and characteristics defined by a map
projection. A common coordinate system is used to spatially register
geographic data for the same area.
- A unique sequence number
automatically generated by ArcInfo for each coverage feature. This
internal number is used to directly access features and to describe
topological relationships between coverage features. It is often referred
to as the record number.
- An integer identifier,
assigned by the user, to relate geographic features and corresponding
attribute data. Cover-ID is an item found in feature
attribute tables, with 'Cover' replaced by the coverage name (e.g.,
for a soils coverage, the Cover-ID would be SOILS-ID). Feature-ID
and User-ID are synonymous terms to Cover-ID.
- 1. A digital version of
a map forming the basic unit of vector data storage in ArcInfo. A
coverage stores geographic features as primary features (such as arcs,
nodes, polygons, and label points) and secondary features (such as
tics, map extent, links, and annotation). Associated feature attribute
tables describe and store attributes of the geographic features.
2. A set of thematically associated data considered as a unit. A coverage
usually represents a single theme such as soils, streams, roads, or
- The coordinates defining
the minimum bounding rectangle (i.e., xmin,ymin and
xmax,ymax) of a coverage or grid. All coordinates for
the coverage or grid fall within this boundary. In ARCPLOT and ARCEDIT,
map extent is often set from the coverage extent. See also BND.
- coverage units
- The units (e.g., feet,
meters, inches) of the coordinate system in which a coverage is stored.
- A method used to index
features that cross tile boundaries. Features that cross tile boundaries
are stored as one or more features in each tile instead of as a single
- The Content Standards
for Spatial Metadata. A document produced by the Federal Geographic
Data Committee (FGDC)
that describes spatial metadata.
- 1. A graphic pointer used
with a mouse to point to a location on a terminal screen.
2. An internal pointer to a record in a table which provides a mechanism
for processing a selected set of records. The cursor is moved one
by one through the set while operations such as display, query and
update are performed.
- 1. In pathfinding, a cycle
is a path or tour beginning and ending at the same node.
2. In tracing, a cycle is a set of arcs forming a closed polygon.
Upstream and downstream directionality are undefinable in a cycle.
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- Data Access Language.
Apple's former standard to allow applications to communicate with
relational databases. DAL is middleware on a network. It is a program
installed on the database server to provide a common SQL access for
all database servers on a network. Apple has licensed this technology
to Independence Technologies, Inc.
- dangle length
- Minimum length allowed
for dangling arcs during the CLEAN process. CLEAN removes dangling
arcs that are shorter than the dangle length.
- An arc having the same
polygon on both its left and right sides and having at least one node
that does not connect to any other arc. It often identifies where
a polygon does not close properly (e.g., undershoot), where arcs don't
connect properly, or where an arc was digitized past its intersection
with another arc (i.e., overshoot). A dangling arc is not always an
error. For example, dangling arcs can represent cul-de-sacs in street
centerline maps. See also dangling
- The endpoint of a dangling
arc not connected to another arc.
- data access security
- Measures taken to control
system users' ability to view or modify data. These measures can include
logical views of data and explicit access rights by group or individual
users. See also access rights.
- A logical collection of
interrelated information, managed and stored as a unit, usually on
some form of mass-storage system such as magnetic tape or disk. A
GIS database includes data about the spatial location and shape of
geographic features recorded as points, lines, areas, pixels, grid
cells, or tins, as well as their attributes.
- database design
- The formal process of
analyzing facts about the real world into a structured database model.
Database design is characterized by the following phases: requirement
analysis, logical design and physical design.
- DATABASE directory
- The same as the Library
Reference workspace. It is the system directory that LIBRARIAN uses
to manage information about a map library. Each map library has one
database directory named DATABASE.
- data conversion
- The translation of data
from one format to another. ArcInfo supports data conversion from
many geographic data formats such as DLG, TIGER, DXF, and DEM.
- data dictionary
- A catalog of all data
held in a database, or a list of items giving data names and structures.
Also referred to as DD/D for data dictionary/directory. Commercial
RDBMSs have online data dictionaries stored in special tables called
- data integrity
- Maintenance of data values
according to data model and data type. For example, to maintain integrity,
numeric columns will not accept alphabetic data. See referential
- 1. The result of the conceptual
design process. A generalized, user-defined view of the data related
2. A formal method of describing the behavior of the real-world entities.
A fully developed data model specifies entity classes, relationships
between entities, integrity rules and operations on the entities.
3. ArcInfo coverages and grids use a georelational data model, a hybrid
data model that combines spatial data (in coverages or grids) and
attribute data (in tables). Other data models used in ArcInfo include
tins, images, and grid.
- data set
- A named collection of
logically related data items arranged in a prescribed manner.
- data type
- The characteristic of
columns and variables that defines what types of data values they
can store. Examples include character, floating point and integer.
- ArcInfo software's link
to relational database management systems (RDBMS). DBI enables ArcInfo
users to access existing commercial databases and take advantage of
the power and capabilities of the RDBMS.
- Locking is a mechanism
by which database systems can prevent conflicting access to data when
multiple users are making requests to the data. See also persistent
management system (DBMS)
- A set of computer programs
for organizing the information in a database. A DBMS supports the
structuring of the database in a standard format and provides tools
for data input, verification, storage, retrieval, query, and manipulation.
- A set of parameters and
control points used to accurately define the three-dimensional shape
of the Earth (e.g., as a spheroid). The datum is the basis for a planar
coordinate system. For example, the North American Datum for 1983
(NAD83) is the datum for map projections and coordinates within the
United States and throughout North America.
- See DATABASE
- See database
- DBMS table
- See attribute
- "Digital Chart of the
World." The first 1:1,000,000-scale digital basemap of the world.
The DCW contains topologically based vector data digitized from the
U.S. Defense Mapping Agency's Operational Navigation Charts.
- Dynamic Data Exchange.
An IAC protocol developed by Microsoft for Windows-based applications.
DDE allows one application to send messages to, and get information
from, other applications in Windows. This is specific to Windows only
(RPC, Remote Procedure Calls, is used in the UNIX environment). DDE
is supported in ArcView Version 2 for the exchange of data with other
business applications without having to convert the data or leave
ArcView. (See IAC.)
- Data definition language.
SQL statements that can be used either interactively or within programming
language source code to define databases and their components.
- See digital
- 1. In allocation, the
potential for using a portion of the supply of a resource or commodity.
2. In spatial interaction, demand is the measure of the need for a
particular type of service or goods that generates a trip to a destination.
For example, the demand for a gallon of milk may generate a trip to
a grocery store.
- The process of restructuring
data model to accommodate operational constraints or system limitations.
- A process of adding vertices
to an arc at specified distances, without altering the arc's shape.
Compare with spline
- Tabular data describing
the characteristics of geographic features. Can include numbers, text,
images, and CAD drawings about features. ArcInfo stores descriptive
data in feature
attribute tables and in related tables. Also referred to as attribute
- In spatial interaction,
the location of the end of a trip. For example, a shop or an office
where a consumer or a worker is going. Destinations are represented
as centers in a network coverage, as points in a point coverage, and
as label points in a polygon coverage.
- 1. A digital representation
of a continuous variable over a two- dimensional surface by a regular
array of z values referenced to a common datum. Digital elevation
models are typically used to represent terrain relief. Also referred
to as 'digital terrain model' (DTM).
2. An elevation database for elevation data by map sheet from the
National Mapping Division of the U.S. Geological Survey (USGS).
3. The format of the USGS digital elevation data sets.
- Digital Geospatial Metadata.
DGM was approved in June 1994 by the Federal Geographic Data Committee
DGM describes the specifications for the content, quality, condition,
and other characteristics of metadata (data about data). The standard
provides a common set of terminology and definitions for the documentation
of geospatial data. DGM establishes the names of data elements and
groups of data elements to be used for these purposes, definitions
of these data elements and groups, and information about the values
that are to be provided for the data elements.
- The Digital Geographic
Information Exchange Standard is produced under authority of NATO's
Digital Geographic Information Working Group. DIGEST is a standard
for digital geographic information which will enable interoperability
and compatibility among national and multinational systems and users.
DIGEST is composed of standards for two digital geographic formats:
ARC Standard Raster Graphic (ASRG) and vector relational format (VRF).
ASRG is very similar to ADRG and can be imported into ArcInfo as an
ADRG file with the ADRGGRID command. The ArcInfo VPFIMPORT and VPFEXPORT
convertors will process the VRF data.
- digital terrain model
- See digital
- 1. To encode geographic
features in digital form as x,y coordinates.
2. The process of using a digitizer to encode the locations of geographic
features by converting their map positions to a series of x,y coordinates
stored in computer files. Pushing a digitizer button records an x,y
coordinate. A digitized line is created by recording a series of x,y
- 1. A device that consists
of a table and a cursor with crosshairs and keys used to digitize
2. Title of the person who uses a digitizing device.
- See digitize.
- See GBF/DIME.
- A network in which each
arc has an associated direction of flow. Direction of flow can be
determined by arc direction (e.g., each arc is digitized so that it
is oriented downstream), a value in an item in the AAT, or through
the use of a selection file.
- A computer term identifying
a location on a disk containing a set of data files and other directories
(subdirectories). Operating systems use directories to organize data.
The location of a directory is specified with a pathname.
- discrete data
- Geographic features containing
boundaries: point, line or area boundaries.
- A storage medium consisting
of a spinning disk coated with a magnetic material for recording digital
- An inexpensive, low-capacity
storage medium, usually measuring 3.5 inches in diameter, often referred
to as a floppy disk.
- The process of removing
boundaries between adjacent polygons that have the same values for
a specified attribute.
- distance-decay function
- In spatial interaction,
the mathematical representation of the effect of distance on the accessibility
and number of interactions between locations. It can be either a power
or an exponential function.
- 1. Digital Line Graph
files from the U.S. Geological Survey (USGS), including data from
the basemap categories such as transportation, hydrography, contours,
and public land survey boundaries.
2. The digital format standards published by USGS for exchanging cartographic
data files and in which the USGS delivers Digital Line Graph data
- Data manipulation language.
SQL statements that can be used either interactively or within programming
language source code to access and retrieve data stored in a database
- In a database, the set
of allowed values for a table column, for example all positive integers.
- Refers to a high level of coordinate accuracy based on the possible
number of significant digits that can be stored for each coordinate.
ArcInfo data sets can be stored in either single- or double-precision
coordinates. Double-precision coverages store up to 15 significant
digits per coordinate (typically, 13 to 14 significant digits), retaining
the accuracy of much less than one meter at a global extent. See also
- In tracing, downstream is the direction along the arcs that is the
same as the direction of flow. Direction of flow is determined by
a user-defined convention. See also directed
- A perspective or panoramic rendering of two-dimensional features
superimposed on a surface.
- Digital terrain model. See digital
- Data Exchange Format. A format for storing vector data in ASCII
or binary files. Used by AutoCAD and other CAD software for data interchange.
DXF files are convertible to ArcInfo coverages.
- dynamic segmentation
- The process of computing the locations of events on linear features
at run time based on event tables for which distance measures are
available. Route-system features and event-handling commands provide
the dynamic segmentation capability within ArcInfo.
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Glossary pages: A-D