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The GIS Glossary -- I-L
This glossary will help familiarize you with terms associated with GIS and ESRI
software. Select a letter to go to that point in the glossary, or use the find tool from
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This page: I J K
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- IAC
- 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. ARC/INFO 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 ARC/INFO 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.
- identity
- 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 and union.
- 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.
- IEEE
- 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).
ARC/INFO and ArcView are fully compatible with network protocols that support IEEE 802.5,
FDDI and X.25 transport standards.
- IGDS
- Interactive Graphics Design Software. Intergraph IGDS file formats can be converted to
and from ARC/INFO coverages.
- IGES
- Initial Graphics Exchange Specification (IGES) is a common data format used for transfer
of CAD data. IGES files can be converted to and from ARC/INFO coverages.
- image
- 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 spectrum.
- 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 ARC/INFO that allows vector and
raster data to be displayed concurrently. Image integrator commands georeference images to
real-world coordinates, display images, and manage image catalogs.
- impedance
- 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).
- index
- Special data structure used in a database to speed searching for records in tables or
spatial features in geographic data sets.
ARC/INFO supports both spatial and attribute
indexes. See also item indexing, cross-tile
indexing and spatial indexing.
- 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.
- INFO
- A tabular DBMS used by ARC/INFO 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 ARC/INFO workspace under a subdirectory named INFO. This subdirectory
contains all feature attribute tables for the set of coverages contained in the workspace.
- INFORMIX
- A relational database management system to which ARC/INFO has access through the
DATABASE INTEGRATOR.
- INGRES
- A relational database management system to which ARC/INFO has access through the
DATABASE INTEGRATOR.
- integer
- A number without a decimal (0, 1, 25, 173, 1032, etc.). Integer values can be less than,
equal to, or greater than zero.
- interaction
- 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 ARC/INFO and for an AML
application to exploit the capabilities of other applications.
- interface
- For data communication, a hardware and software link that connects two computer systems,
or a computer and its peripherals.
- internal number
- See Cover#.
- Internet
- 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 ARC/INFO users a way to exchange technical
questions and information.
- interpolation
- The estimation of z values of a surface at an unsampled
point based on the known z values of surrounding points.
- intersect
- 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.
- ISDN
- 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.
- ISO
- 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.
- isoline
- A line on a surface connecting points of equal value.
- item
- 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.
- ITUM
- 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.
- join
- See relational join.
- label point
- See point.
- LAN
- 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.
- Landsat
- 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 ARC/INFO and ArcView.
- latitude-longitude
- 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.
- lattice
- 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.
- layer
- 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 library.
- 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 ARC/INFO uses to represent contiguity between polygons.
Left-right supports analysis functions such as adjacency. See also topology.
- legend
- 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.
- LIBRARIAN
- 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.
- library
- A collection of spatially related ArcStorm or LIBRARIAN layers. A library has a spatial
extent which applies to all layers in the library.
- line
- 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 boundary lines).
2.
A single arc in a coverage.
3. A line on a map (e.g., a neatline).
- line-in-polygon
- 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.
- line symbol
- 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 ARC/INFO by arcs or by the
route-system feature class.
- link
- A coverage feature class; links are two-point segments that represent from- and
to-locations for the rubber sheeting adjustment process.
- literal
- 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.
- logical expression
- 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 expression.
- logical selection
- 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 transaction
- 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.
- longitude
- See latitude-longitude.
- lookup table
- 1. A special tabular data file containing additional attributes for features stored in
an associated feature attribute 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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