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-- GIS
Glossary
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GIS Glossary:
A-D E-H
I-L M-P
Q-S T-Z
- AAT
-
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 attribute table.
- acceptance test
-
A test for evaluating a
newly purchased system’s performance and conformity to specifications.
- access time
-
A measure of the time
interval between the instant that data are called from storage and the
instant that delivery is complete.
- accuracy
-
Conformity with a standard
of correctness in measurement. Accuracy relates to the quality of a result
and is distinguished form precision which relates to the quality of the
operation by which the result is obtained.
- 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
directory.
- accessibility
-
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
'read/write'.
- 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.
- acoustic coupler
-
A device that enables a
computer terminal to be linked to another over the telephone system via
the handset of a conventional telephone.
- active sensors
-
Active sensors emit their
own energy that travels from the instrument to the target, returns to the
sensor, and is used to produce an image of the target.
- 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.
- address range
-
Street numbers running from
lowest to highest along a street or street segment. Address ranges are
generally stored as fields in the attribute table of a street data layer
and are used for geocoding.
- addressable point
-
A position on a visual
display unit (VDU) that can be specified by absolute coordinates.
- addressability
-
The number of positions
(pixels) in the X and Y axes on a VDU or graphics screen.
- ADS
-
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.
- aerial photograph
-
A photograph of the earth's
surface taken with a camera mounted in an airplane or balloon. Used in
cartography to provide geographical information for basemaps.
- algorithm
-
Statement of the steps to
be followed in the solution of a problem.
- aliasing
-
The occurrence of jagged
lines on a raster-scan display image when the detail exceeds the
resolution of the screen.
- allocation
-
The process of assigning
arcs in a network to the closest center until the maximum impedance or
resource capacity of the center is reached.
- alphanumeric code
-
Machine-processable
letters, numbers and special characters, hence alphanumeric screen.
Alphanumeric keyboard for displaying and entering alphanumeric characters.
-
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.
- analog
-
A continuously varying
electronic signal (contrast with Digital).
-
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 and
spatial analysis.
- annotation
-
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.
- application
-
A task addressed by a
computer system.
-
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
topology.
- archive
-
A preserved collection of
historical information purged from an ArcStorm database.
- ArcStorm
-
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 INTEGRATOR.
-
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
-
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.
- array
-
A series of addressable
data elements in the form of a grid or matrix.
-
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.
- aspect
-
The compass direction
toward which a slope faces, measured in degrees from North in a clockwise
direction.
- ASRG
-
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 attribute table.
- autocorrelation,
autocovariance
-
Statistical concepts
expressing the degree to which the value of an attribute at spatially
adjacent points co-varies with the distance separating the points.
- Automated Facilities
Management (AM/FM)
-
A system that integrates
automated mapping with facilities management (e.g., Mapping/Facilities
management of power lines, utilities, or energy services). AM/FM provides
digital or computer-based storage, management, retrieval, and display of
urban data for cadastral mapping and utilities management.
- azimuth
-
The horizontal direction of
a vector, measured clockwise in degrees of rotation from the positive
y-axis, for example, degrees on a compass.
- backup
-
A copy of a file, a set of
files, or whole disk for safekeeping in case the original is lost or
damaged.
- band
-
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.
- bandwidth
-
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.
- base map
-
Mapped data which seldom
change and which are used repeatedly for locational reference and control.
It also establishes the lowest common denominator for map scale,
coordinate system, and projection for other maps in a GIS database.
Contrast with thematic map. Examples include topographic and planimetric
maps.
- base table
-
A table that is physically
stored in the database. Compare with
view.
- batch processing
-
The processing of a group
of similar jobs on the computer without operator intervention.
- baud rate
-
A measure of the speed of
data transmission between computer and other devices, measured in bits per
second.
- benchmark
-
A reference point for
measurements, normally one that is used for elevation reference.
- benchmark test
-
A test to evaluate the
capabilities of a computer system in terms of performance and ability to
meet customer requirements.
- binary coded decimal
-
The expression of each
digit of a decimal number in terms of a set of bits.
-
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.
- bit map
-
A pattern of bits (i.e.,
ON/OFF) on the grid stored in memory and used to generate an image on a
raster scan display.
- bit plan
-
A gridded memory in a
graphics device used for storing information for display.
- bits per inch (BPI)
-
The density of bits
recorded on a magnetic tape. 800, 1600 and 6500 are common standards.
- boolean operators (BPI)
-
Search strategy for
information retrieval based on the use of the logical operators AND
(union), OR (intersection), NOT (complement), and XOR (exclusion) to
represent symbolic relationships.
- BLOB
-
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 extent.
-
1. 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 selection.
- 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.
-
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.
- buffer
-
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).
- bug
-
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.
- C / C++
-
A high level programming
language.
- CAD/CAM
-
Computer-Aided
Design/Computer Aided Manufacturing. Several CAD/CAM systems also include
major features for GIS and automated mapping.
- 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.
- cadastral parcel
-
The smallest legally
defined piece of land. Used for recording ownership and related
attributes.
- cadastral survey
-
A boundary survey taken for
the purpose of taxation.
- cadastre
-
A survey that creates,
defines, retraces, or re-establishes the boundaries and subdivisions of
public lands and private estates. The ownership, characteristics, and
value of private lands are recorded for taxation purposes.
- calibration
-
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
items.
- capacity
-
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.
-
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.
- cartographic modeling
-
The use of basic GIS
manipulation functions or tools in a logical sequence to solve spatial
problems.
- cartography
-
The science of map making,
including the art and technology of map-making.
- cartridge disk
-
A type of magnetic memory
disk enclosed in a plastic cartridge.
- CASE
-
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
process.
- cathode ray tube (CRT)
-
An electronic screen for
displaying information or graphics. Also called a visual display device
(VDU).
-
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.
- 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.
- census block
-
The smallest unit used by
the U.S. Census Bureau for reporting census data and for generating
geographic base files such as DIME and TIGER® files. A block is enclosed
by any natural or human-made features that form a logical boundary, such
as roads, political boundaries, or shorelines. .
-
A discrete location that
has a supply of a resource or commodity. In spatial interaction, a center
is consider to have attractiveness.
- central processing unit (CPU)
-
The part of the computer
that controls the whole system..
- centroid (CPU)
-
The mathematical or
geographical center point of a polygon or the midpoint of a line. It is
described as an x, y coordinate..
- CGM
-
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.
- chain (CPU)
-
A sequence of coordinates
defining a complex line or boundary. See Arc, and String. .
- change detection
-
Is the comparison of two
images acquired at different times of the same area. Differences found
between these two images can provide information concerning what
alterations have occurred over time.
- 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 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 on.
- checkin
-
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 are
released.
- checkout
-
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.
- client/server
-
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.
- clip
-
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.
- choropleth map
-
A map with areas colored or
shaded such that the darkness or lightness of an area symbol is
proportional to the density of the mapped phenomena or is symbolic of the
class.
- classification
-
Process of assigning
individual observations of features into groups, categories, or classes.
- clearinghouse
-
A place that stores and
disseminates data.
- clip
-
The process of extracting a
portion of a coverage or map from a larger coverage, much like a cookie
cutter.
- code
-
A set of specific symbols
and rules for representing data and programs so that they can be
understood by the computer. See ASCII, FORTRAN, PASCAL, etc.
-
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.
- coincidence analysis
-
Process of examining the
co-occurrence of mapped phenomena.
-
The vertical dimension of a
table. A column has a name and a data type applied to all values in the
column.
- command
-
A specific instruction to a
computer program, issued by the user to perform a desired action.
-
A software product that
allows the user to type in commands at a prompt. Contrast to
forms interface.
-
To make permanent any
changes made during a database transaction. Compare with
roll back.
- composite map
-
A single map created by
joining together several separately digitized maps..
- computer aided drawing (CAD)
-
Software with the
capability of performing standard engineering drawing and architecture
design functions. It is graphically oriented rather than geographically
based. Unlike a GIS, the database is generally not structured to allow
spatial analysis. However, some data developed in CAD systems can be
incorporated into a GIS. .
- computer aided mapping (CAD)
-
Software with the
capability of performing standard mapping functions, typically mapping
(CAM) using a vector format. Unlike a GIS, it cannot analyze or process
the database. .
- 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
- conflation
-
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
operations.
- connectivity
-
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 topology.
- constraints
-
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.
- contiguity
-
The topological
identification of adjacent polygons by recording the left and right
polygons of each arc. See also
polygon-arc topology.
- 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).
- contour
-
A line connecting points of
equal surface value.
- contour interval
-
The difference in surface
values between contours.
- coordinate
-
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.
- corridor analysis
-
A type of proximity
analysis that utilizes specified distances or buffers along a line (e.g.,
amount of timber within 50 feet of a proposed power transmission line).
See buffer.
- cost benefit analysis
-
A comparison of the costs
and benefits of the current system of processes versus a proposed GIS. A
cost-benefit analysis is developed to assist with making an acquisition
decision.
-
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.
- coverage
-
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 land use.
-
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.
- cross tabulation
-
Comparison of attribute
data by location in two or more map layers. Results are given in a tabular
report format.
-
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
feature.
-
The Content Standards for
Spatial Metadata. A document produced by the Federal Geographic Data
Committee (FGDC)
that describes spatial metadata.
- cursor
-
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.
- cycle
-
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.
- DAL
-
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 node.
-
The endpoint of a
dangling arc not connected to another arc.
- data (singular datum)
-
Facts about real-world
entities, organized for analysis. Includes results of observations or
measurements of such entities. Three components of a datum are of direct
relevance to GIS: (1) attribute information that describes the substance,
characteristics, variables, values, and similar qualities of the entity;
(2) geographical information that describes the position of the entity in
space relative to other things in space; and (3) temporal information that
describes the instant or period of time during which the entity is at a
defined location or in an observed state or condition (attribute).
- 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.
- database
-
One or more structured sets
of persistent data, managed and stored as a unit and generally associated
with software to update and query the data. A simple database might be a
single file with many records, each of which references the same set of
fields. Examples of popular databases include dBase®, Oracle®, and
SQLServer®. A GIS database includes data about the spatial locations and
shapes of geographic features recorded as points, lines, areas, pixels,
grid cells, or TINs, as well as the 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 capture
-
Operations that are
required to encode data in a computer readable digital form (e.g.,
digitizing, scanning). See also data input.
- 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
system tables.
- data encoding
-
To apply a code to
represent individual data or groups of data. .
- 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 integrity.
-
1. The result of the
conceptual design process. A generalized, user-defined view of the data
related to applications.
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 quality
-
The degree of excellence
exhibited by the data in relation to a correct portrayal of the actual
phenomena.
- data set
-
A named collection of
logically related data items arranged in a prescribed manner.
- data standardization
-
The process of achieving
agreement on common data definitions, representation, and structures to
which all data layers and items must conform.
- 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 lock.
-
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.
- datum
-
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.
- DBI
-
See DATABASE
INTEGRATOR.
- DBMS
-
See
database management system.
- DBMS table
-
See
attribute table.
- DCW
-
"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.)
- DDL
-
Data definition language.
SQL statements that can be used either interactively or within programming
language source code to define databases and their components.
- delineation
-
The legal description of
the locations of points that mark the boundaries of a cadastral parcel.
- DEM
-
See digital
elevation model.
- demand
-
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.
- demarcation
-
The field measurements
(e.g., land survey) that determine the physical locations of boundary
markers of cadastral parcels.
- denormalization
-
The process of
restructuring a
normalized 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 and
grain tolerance.
-
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 data.
- destination
-
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.
- differential correction
-
A technique for increasing
the accuracy of GPS measurements by comparing the readings of two
receivers, one roving, the other fixed at a known location.
-
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 (FGDC).
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.
- DIGEST
-
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 image
-
[REMOTE SENSING,
PHOTOGRAMMETRY, GRAPHICS] An image stored in binary form and divided into
a matrix of pixels, each consists of one or more bits of information that
represent either the brightness, or brightness and color, of the image at
that point. .
- digital terrain model
-
See digital
elevation model.
-
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 coordinates.
- digitizer
-
1. A device that consists
of a table and a cursor with crosshairs and keys used to
digitize geographic features.
2. Title of the person who
uses a digitizing device.
- digitizing
-
See
digitize.
- DIME
-
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.
- directory
-
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.
- direichlet tessellation
-
The process of splitting up
a study area such that all points in the sample area are grouped into
tiles according to the minimum distance between them and a previously
sampled point. Also known as Thiessen or Voronoi polygons.
- discrete data
-
Geographic features
containing boundaries: point, line or area boundaries.
- disk
-
A storage medium consisting
of a spinning disk coated with a magnetic material for recording digital
information.
- diskette
-
An inexpensive,
low-capacity storage medium, usually measuring 3.5 inches in diameter,
often referred to as a floppy disk.
- dissolve
-
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.
- distributed processing
-
The placement of hardware
processors where needed, instead of concentrating all computer power in a
large central CPU.
- DLG
-
1. Digital Line Graph files
from the U.S. Geological Survey (USGS), including data from the base map
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 sets.
- DML
-
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
management system.
- domain
-
In a database, the set of
allowed values for a table column, for example all positive integers.
- DOP - Dilution of Precision
-
Also Geometric Dilution of
Precision (GDOP) [GPS] An indicator of satellite geometry for a
constellation of satellites used to determine a position. Positions with a
higher DOP value generally constitute poorer measurement results than
those with lower DOP. Factors determining the total GDOP for a set of
satellites include, to name a few, PDOP (Positional DOP), HDOP (Horizontal
DOP), VDOP (Vertical DOP), and TDOP (Time DOP).
-
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
single precision.
- downstream
-
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 network.
- drape
-
A perspective or panoramic
rendering of two-dimensional features superimposed on a surface.
- drum plotter
-
A device with a rotating
cylindrical drawing surface and paper reels for plotting graphic images on
a continuous roll of paper.
- drum scanner
-
A device for converting
maps to digital form automatically.
- DTM
-
Digital terrain model. See
digital elevation model.
- dual independent map encoding
-
For the 1980 census, the
U.S. Census Bureau produced Geographic Base Files (GBF) and Dual
Independent Map Encoding (DIME) files, containing census geographic
statistical codes and co-ordinates of line segments for most metropolitan
areas. DIME files provide a schematic map of a city's streets, address
ranges, and geostatistical codes relating to the Census Bureau's tabular
statistical data. DIME was replaced by TIGER® for the 1990 Census.
- DXF
-
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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