The GIS Glossary
Environmental Systems Rearch Institute, Inc.
January 2, 1996
This glossary will help familiarize you with terms associated with
GIS and ESRI software. Select a character below to go to that
point in the glossary or u the find tool from your browr.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
AAT
Arc attribute table. A table containing attributes for arc coverage features. In addition to ur-defined attributes, the AAT contains the from and to nodes, the left and right polygons, the length, an internal quence number and
a feature identifier. See also feature attribute table.
ACCESS directory
The system directory that LIBRARIAN us to store the files that manage access to the library. Each library has an ACCESS directory located in the library's DATABASE directory.
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An aggregate measure of how reachable locations are from a given location. The ACCESSIBILITY command
如何升级bioscomputes values for accessibility as a function of the distance between locations and an empirically derived
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access rights
The privileges accorded a ur for reading, writing, deleting, updating and executing files on a disk. Access rights are stated as `no access', `read only' and `read/write'.
戚风纸杯蛋糕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 address can be matched to
a street coverage that contains address creating a point coverage of where the students live.
ADS
1. Arc Digitizing System. A simple digitizing and editing system ud to add arcs and label points to a coverage.
2. A command at the Arc: prompt that starts an ADS ssion.
allocation
The process of assigning arcs in a network to the clost center until the maximum impedance or resource capacity of the center is reached.
AML
ARC Macro Language. A high-level algorithmic language for generating end-ur applications. Features include the ability to create on-screen menus, u and assign variables, control statement execution, and get and u map or page unit coordinates. AML includes an extensive t of commands that can be ud interactively or in AML programs (macros) as well as commands that report on the status of ARC/INFO environment ttings.
analysis
Analysis is the process of identifying a question or issue to be addresd, modeling the issue, investigating model results, interpreting the results, and possibly making a recommendation. See model and spatial analysis.
annotation
1. Descriptive text ud to label coverage features. It is ud for display, not for analysis.
2. One of the feature class in a coverage ud 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.
ANSI
American National Standards Institute is a national coordinator of voluntary standards activities, and an approval organization and clearinghou for connsus standards in the United States. ANSI works cloly 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 t of system calls or routines for application programs to
access rvices 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/rver computing. ArcView provides this rvice to ARC/INFO urs.
arc
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 ud to reprent 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 n ode.
arc-node topology
The topological data structure ARC/INFO us to reprent 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 topology.
archive
A prerved collection of historical information purged from an ArcStorm databa.
ArcStorm
ArcStorm (ArcStorageManager) is a data storage facility and transaction manager for ARC/INFO data. ArcStorm manages a feature-oriented databa that can be cloly integrated with databa systems supported by
ARC/INFO's DATABASE INTEGRATOR.
ArcStorm databa
An ArcStorm databa is a collection of libraries, layers, INFO tables and external DBMS tables. Data stored in an ArcStorm databa benefit from the transaction management and data archiving capabilities of ArcStorm.
ArcTools
ArcTools is a collection of ARC/INFO productivity tools implemented through an A ML-bad (ARC Macro
Language) graphical ur interface. ArcTools provides a ur-friendly approach to commonly ud ARC/INFO operations and functions.
金砖五国峰会area
polygons (region). Examples: states, counties, lakes, land-u areas, and census tracts.
2. The size of a geographic feature measured in unit squares. ARC/INFO stores an area measure for each polygon
and region.
ASCII
American Standard Code for Information Interchange. A t of codes for reprenting alphanumeric information
(e.g., a byte with a value of 77 reprents a capital M). Text files, such as tho created with the text editor of a
computer system, are often referred to as ASCII files.
aspect
The compass direction toward which a slope faces, measured in degrees from North in a clockwi direction.
ASRG
ARC Standard Raster Graphic. Raster graphic data transformed to the Equal ARC-cond Raster Chart/Map
(ARC) Projection System. See SRG. ASRG (using RGB) is very similar to DMA (Defen Mapping Agency)
ADRG (ARC Digitized Raster Graphic). ADRG files can be imported into ARC/INFO with the ADRGGRID
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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.
attractiveness
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 the factors.
attribute
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 ur-assigned identifier (e.g., the attributes of a well might include depth and gallons per minute).
2. A column in a databa table. See also item.
attribute table
An INFO or other tabular file containing rows and columns. In ARC/INFO, attribute tables are associated with a class of geographic features, such as wells or roads. Each row reprents a geographic feature. Each column
reprents one attribute of a feature, with the same column reprenting the same attribute in each row. See also feature attribute table.
azimuth
The horizontal direction of a vector, measured clockwi in degrees of rotation from the positive y-axis, for
example, degrees on a compass.
B
backup
A copy of a file, a t of files, or whole disk for safekeeping in ca the original is lost or damaged.
band
One layer of a multispectral image reprenting 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 ur-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 ven or more bands.
band parate
An image format that stores each band of data collected by multispectral satellite scanning instruments in a
parate file.
bandwidth
A measure of the volume of data that can flow through a communications link. Image data tend to exist as large
data ts; thus moving image data ts from one computer to another requires high bandwidth or performance will be slowed. Also known as throughput.
ba map
A map containing geographic features ud for locational reference. Roads, for example, are commonly found on
ba maps.
ba table
A table that is physically stored in the databa. Compare with view.
baud rate
A measure of the speed of data transmission between computer and other devices, measured in bits per cond.
bit
The smallest unit of information that a computer can store and process. A bit has two possible values, 0 or 1,小狗英语
which can be interpreted as YES/NO, TRUE/FALSE, or ON/OFF. See also b yte.
BLOB
Binary large object. The data type of a column in an RDBMS table which can store large image or textual data as attributes.
BND
The file in a coverage or grid which contains the coverage extent.
Boolean expression
1. A type of expression that reduces to a true or fal (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 lection.
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 into tiles.
breakline
A linear feature that defines and controls the surface behavior of a t in 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.
buffer
A zone of a specified distance around coverage features. Both constant- and variable-width buffers can be
generated for a t of coverage features bad 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 uful for proximity analysis (e.g., find all stream gments within 300 feet of a propod logging area).
bug
An error in a computer program or in a piece of electronics that caus it to malfunction.
byte
A memory and data storage unit compod 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 reprent integer
numbers or ASCII characters (e.g., a byte with an ASCII value of 77 reprents a capital M). A collection of
bytes (often 4 or 8 bytes) reprents real numbers and integers larger than 255.
C
CAD
Computer-aided design. An automated system for the design, drafting, and display of graphically oriented
information.
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.
calibration
The process of choosing attribute values and computational parameters so that a model properly reprents 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 items.
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capacity
The maximum resource that can be assigned (allocated) to or be rviced by a c enter. 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.
CASE
Computer-Aided Software Engineering. CASE tools are defined programming rules for applying engineering
principles, methods, techniques, and concepts. The 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 ts and supporting the entire software life cycle process.
CCITT
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 ts international communications recommendations concerning
standardization of data interfaces, modems, and data networks. ARC/INFO is fully compliant with CCITT Group IV, the Standard for raster data compression. ARC/INFO supports the following T IFF 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.
CD-ROM
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.
cell
See grid cell.
center
A discrete location that has a supply of a resource or commodity. In spatial interaction, a center is consider to have
attractiveness.
CGM
Computer Graphics Metafile is a graphic image exchange standard, ANSI: x3.122-1986, ISO: 8632-1986, for
graphic output file format. ARC/INFO, ArcView Version 2, and PC ARC/INFO support CGM.
character
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 reprented 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 on.
checkin
Checkin is the act of returning ArcStorm data which was previously checked out for update purpos. When
