GIS Definitions: I-L
Definitions of some commonly used GIS (Geographic Information System) terms.
I J K
L Full glossary:
- Interapplication communication.
The capability of one computer program to communicate with another
program. With IAC, two (or more) programs can execute simultaneously,
share data, and make requests of each other. ArcInfo Version 7 and
ArcView Version 2 support IAC. IAC tools in AML (ARC Macro Language)
support real-time GIS, a network GIS process server, interoperability,
and open integration between ArcInfo and other applications. In a
client/server environment the command references on the client side
are IACCONNECT, IACDISCONNECT, and IACREQUEST; on the server side
are IACOPEN, IACCLOSE, and &IACRETURN.
- The topological
overlay of a coverage (input) with a polygon coverage (identity).
For each feature in the input coverage, the intersection with identity
features is determined, creating new features of the same feature
class as the input coverage. For example, a road (input coverage,
arc feature class) passing through two counties (identity coverage)
would be split into two arc features, each with the attributes of
the road and the county it passes through. Compare with intersect
- identity link
- A coverage link whose
from-location is the same as its to-location. Used to control rubber
sheeting and adjustment operations. Identity links act as nails to
hold down the point location during adjustment. See also link.
- Institute of Electrical
and Electronics Engineers. IEEE Standard 1003.1-1990 (aka POSIX.1)
defines C program interfaces for the operating system that enable
source code portability beyond the ANSI C definition (see POSIX).
ArcInfo and ArcView are fully compatible with network protocols that
support IEEE 802.5, FDDI and X.25 transport standards.
- Interactive Graphics Design
Software. Intergraph IGDS file formats can be converted to and from
- Initial Graphics Exchange
Specification (IGES) is a common data format used for transfer of
CAD data. IGES files can be converted to and from ArcInfo coverages.
- A graphic representation
or description of a scene, typically produced by an optical or electronic
device. Common examples include remotely sensed data (e.g., satellite
data), scanned data, and photographs. An image is stored as a raster
data set of binary or integer values that represent the intensity
of reflected light, heat, or other range of values on the electromagnetic
- image catalog
- An organized set of spatially
referenced, possibly overlapping, images that can be accessed as one
logical image. An image catalog is a group of images on disk, each
referenced by a record in an INFO data file. At a minimum, items in
the data file include the image pathname and the bounding coordinates
xmin,ymin and xmax,ymax.
- image integrator
- A collection of image
management and display tools in ArcInfo that allows vector and raster
data to be displayed concurrently. Image integrator commands georeference
images to real-world coordinates, display images, and manage image
- The amount of resistance
(or cost) required to traverse a line from its origin node to its
destination node or to make a turn (i.e., move from one arc through
a node onto another arc). Resistance may be a measure of travel distance,
time, speed of travel times the length, and so on. Higher impedance
indicates more resistance to movement, with 0 indicating no cost.
Often, a negative impedance value indicates a barrier. Impedance is
used in network routing and allocation. An optimum path in a network
is the path of least resistance (or lowest impedance).
- Special data structure
used in a database to speed searching for records in tables or spatial
features in geographic data sets.
ArcInfo supports both spatial
and attribute indexes. See also item
indexing and spatial
- index coverage
- The polygon coverage that describes, and is used as a spatial index
for, the tile structure of a layer. Each polygon in an index coverage
corresponds to a tile.
- A tabular DBMS used by ArcInfo to store and manipulate feature
attribute tables and other related tables.
- INFO database
- The contents of a set of INFO data files, feature attribute tables,
and related files stored in each ArcInfo workspace under a subdirectory
named INFO. This subdirectory contains all feature attribute tables
for the set of coverages contained in the workspace.
- A relational database management system to which ArcInfo has access
through the DATABASE INTEGRATOR.
- A relational database management system to which ArcInfo has access
through the DATABASE INTEGRATOR.
- A number without a decimal (0, 1, 25, 173, 1032, etc.). Integer
values can be less than, equal to, or greater than zero.
- Interaction is a measure of the estimated number of trips that will
be generated between origins and destinations for a particular activity.
Interactions depend upon the properties of the origin to generate
a trip, the property of the destination to attract a trip and the
cost of traveling between them.
- interaction matrix
- A generated INFO file containing the number of interactions occurring
between a set of origins and destinations. The interaction matrix
can be analyzed to make trade-area maps.
- inter-application communication (IAC)
- A technology that enables software applications on remote or local
machines to communicate with each other. IAC makes it possible to
develop applications that seamlessly integrate the capabilities of
a number of programs by providing a way for external applications
to request services of ArcInfo and for an AML
application to exploit the capabilities of other applications.
- For data communication, a hardware and software link that connects
two computer systems, or a computer and its peripherals.
- internal number
- See Cover
- An international consortium of wide area networks that operate using
a standard set of addresses allowing machine-to-machine connectivity
on a global scale. The Internet is an outgrowth of a Defense Advanced
Research Projects Agency (DARPA) research project in the early 1970s
to provide connectivity between scientists running computer simulations
in different locations. Additional regional, private, and public networks
have joined the Internet over time. At this point there are over two
million computers that now have direct access to the resources on
the Internet. ESRI operates a discussion group on the Internet called
ESRI-L. ESRI-L is open to the general public and is available to any
Internet subscriber. It was established to give ArcInfo users a way
to exchange technical questions and information.
- The estimation of z values of a surface
at an unsampled point based on the known z values of surrounding
- The topological integration of two spatial data sets that preserves
features that fall within the area common to both input data sets.
See also identity and union.
- Integrated Services Digital Network, provides WAN (see WAN)
combined transmission of analog and digital services. ISDN is offered
as a Basic Rate Service on either one or two channels for WAN services
of either 64 kbps or 128 Kbps. ISDN services are available from a
long-distance telephone company.
- The International Organization for Standardization. A worldwide
federation of national standards bodies (e.g., ANSI
from the U.S.) that develops international standards. A Technical
Committee (ISO/TC211) is developing international Geographic Information/Geomatics
standards. Among many other computing standards, ISO maintains an
SQL standard and is developing an extended version, SQL3, which will
support queries on geographic data sets.
- ISO 8211
- The third of three parts of the SDTS (see SDTS)
that specifies data transfer implementation (i.e., encoding method).
ISO 8211 is a general-purpose, media-independent interchange standard
whose variable length records may be written on any medium that is
able to accept them, including communications lines.
- ISO 9000
- Established in 1987, ISO 9000 is an international set of five related
standards for qualification of global quality assurance and quality
control standards. Adherence is accomplished through an application
process for ISO 9000 certification in company standards for inspecting
production processes, updating records, maintaining equipment, training
employees and handling customer relations. The governing international
consortium is recognized worldwide.
- ISO 9660
- Volume and file structure of CD-ROM for Information Interchange.
A standard for the organization of data on CD-ROM media established
by the International Standards Organization.
- A line on a surface connecting points of equal value.
- A column of information in an attribute table, for example, a single
attribute of a record in an INFO data file.
- item indexing
- A means of accelerating logical queries and tabular 'relates' by
creating an index on an item in a database table.
- Integrated Terrain Unit Mapping is an example of integrated data
management. It is the process of adjusting terrain unit boundaries
so that there is increased coincidence between the boundaries and
occurrences of interdependent terrain variables such as hydrography,
geology, physiography, soils and vegetation units.
- See relational join.
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- label point
- See point.
- Local area network. Computer
data communications technology that connects computers at the same
site. Computers and terminals on a LAN can freely share data and peripheral
devices, such as printers and plotters. LANs are composed of cabling
and special data communications hardware and software.
- A series of satellites
that produce images of the earth. The Landsat remote sensing satellite
program was developed by NASA (National Aeronautics and Space Administration).
Landsat data are provided in .BIL (band interleaved by line) or .BIP
(band interleaved by pixel) formats. BIL and BIP are supported by
ArcInfo and ArcView.
- A spherical reference
system used to measure locations on the Earth's surface. Latitude
and longitude are angles measured from the Earth's center to locations
on the Earth's surface. Latitude measures angles in a north-south
direction. Longitude measures angles in the east-west direction.
- A surface
representation that uses a rectangular array of mesh
points spaced at a constant sampling interval in the x and y directions
relative to a common origin. A lattice is stored as a grid, but represents
the value of the surface only at the mesh points rather than the value
of the entire cell.
- A thematic set of spatial
data described and stored in an ArcStorm database or a LIBRARIAN map
library. Layers organize a database or map library by subject matter
(e.g., soils, roads, and wells). Conceptually, layers in a database
or map library environment are exactly like coverages. See also ArcStorm
database and map
- layer index
- See cross-tile indexing.
- least-cost path
- The path, among possibly
many, between two points which has the lowest traversal cost, where
cost is a function of time, distance, or other user-defined factors.
See also impedance.
- left-right topology
- The topological data structure
ArcInfo uses to represent contiguity between polygons. Left-right
supports analysis functions such as adjacency. See also topology.
- 1. The reference area
on a map that lists and explains the colors, symbols, line patterns,
shadings, and annotation used on the map. The legend often includes
the scale, origin, orientation, and other map information.
2. The symbol key used to interpret a map.
- A set of software tools
to manage and access large geographic data sets in a map library.
LIBRARIAN commands create and define a map library, move
data in and out of a library, query the data in a map library, and
display the results of a query.
- A collection of spatially
related ArcStorm or LIBRARIAN layers. A library has a spatial extent
which applies to all layers in the library.
- 1. A set of ordered coordinates
that represents the shape of geographic features too narrow to be
displayed as an area at the given scale (e.g., contours, street centerlines,
or streams), or linear features with no area (e.g., state and county
2. A single arc
in a coverage.
3. A line on a map (e.g., a neatline).
- A spatial operation in
which arcs in one coverage are overlaid with polygons of another coverage
to determine which arcs, or portions of arcs, are contained within
the polygons. Polygon attributes are associated with corresponding
arcs in the resulting line coverage.
- A symbol for drawing coverage arcs.
- linear event
- See event.
- linear feature
- A geographic feature that
can be represented by a line or set of lines. For example, rivers,
roads within a pizza delivery area, and electric and telecommunication
networks are all linear features. Linear features are represented
in ArcInfo by arcs or by the route-system feature class.
- A coverage feature class;
links are two-point segments that represent from- and to-locations
for the rubber sheeting adjustment process.
- A string, a number, or
a date which directly represents a constant value. 'XYZ123', '1234'
and '6/10/57' are examples of a string literal, a numeric literal
and a date literal, respectively.
- local area network
- See LAN.
- log file
- A coverage or workspace
history file containing a list of all commands used to operate on
a coverage or all commands used in the workspace.
- logical connector
- One of the reserved words
AND, OR and XOR used to build complex logical
expressions in a query.
- A combination of items,
system items, system variables, literals and arithmetic logical operators
from which a value of TRUE or FALSE is derived; for example:
$RECNO LE $NUM1
HRS-WRKD * HRLY-WAGE GE 600 AND $MONTH EQ 5
$NUM1 LE 100
- logical operator
- Another term for Boolean
operator. See Boolean
- The process of selecting
a subset of features from a coverage using logical expression that
operates on the attributes of coverage features (e.g., AREA GT 16000).
Only those features whose attributes meet the criteria are selected.
Also known as feature selection by attribute.
- Long transactions support
applications where changes to a database might span several days,
weeks or months and may involve several sessions. Many planning and
design activities, such as subdivision development, require long transactions.
- See latitude-longitude.
- lookup table
- 1. A special tabular data
file containing additional attributes for features stored in an associated
table. The table can be an external attribute table or an INFO
table that describes coverage features.
2. A special lookup table in which numeric item values are classified
into categories. For example, well depth can be recorded explicitly
in the feature attribute table, but displayed and used as a set of
classes, such as 0 to 250 feet, 251 to 500 feet, and so on. An INFO
lookup table contains at least two items: the relate item and an item
named either SYMBOL or LABEL.
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Glossary pages: A-D