GIS Glossary/I

GIS Glossary

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ICAO
Acronym for International Civil Aviation Organization. A member organization that represents the worldwide body of nations for standardizing flight rules, regulations, and requirements.

icon
In MOLE, the innermost graphic component of a graphic. Icons represent the Function ID position of a Symbol ID code.

ID
A unique character string or numeric value associated with a particular object.

IDE
Acronym for integrated development environment. A software development tool for creating applications, such as desktop and Web applications. IDEs blend user interface design and layout tools with coding and debugging tools.

identifier
A unique character string or numeric value associated with a particular object.

identify
In ArcGIS, a tool that, when applied to a feature (by clicking it), opens a window showing that feature's attributes.

identity
In geoprocessing, a topological overlay that computes the geometric intersection of two datasets. The output dataset preserves all the features of the first dataset plus those portions of the second (polygon) dataset that overlap the first. For example, a road passing through two counties would be split into two arc features, each with the attributes of the road and the county it passes through.

identity link
An anchor that prevents the movement of features during rubber sheeting.

IDispatch
A generic COM interface that has methods allowing clients to ask which members are supported. Classes that implement IDispatch can be used for late binding and DispID binding, which is a form of early binding.

IDL
Acronym for Interface Definition Language. A language used to define COM interfaces. The Microsoft implementation of IDL may also be referred to as MIDL or Microsoft IDL.

IDW
An interpolation technique that estimates cell values in a raster from a set of sample points that have been weighted so that the farther a sampled point is from the cell being evaluated, the less weight it has in the calculation of the cell's value.

IFSAR
Acronym for interferometric synthetic aperture radar. A dual-antenna radar sensor mounted on an airborne or space-borne platform that collects a remotely sensed radar image, called an interferogram. There is a measured energy shift between the signals received by each antenna, and this interference can be colorized to measure elevation or changes in the topography on the earth's surface.

IID
Acronym for interface identifier. A string that provides the unique name of an interface. An IID is a type of globally unique identifier (GUID).

illumination
The light incident on a surface or object, either natural or artificial, as determined by the surface's slope and aspect and by the sun's azimuth and altitude.

image
A representation or description of a scene, typically produced by an optical or electronic device, such as a camera or a scanning radiometer. Common examples include remotely sensed data (for example, satellite data), scanned data, and photographs.

image catalog
A collection of raster datasets defined in a table of any format, in which the records define the individual raster datasets that are included in the catalog. Raster catalogs can be used to display adjacent or overlapping raster datasets without having to mosaic them together into one large file. In ArcView 3.x, raster catalogs were called image catalogs.

image coordinate
An x,y coordinate pair specifying the location of a pixel, or cell, in terms of its row and column position. The x-coordinate gives the column number (commonly starting from 0 at the left edge of the data), and the y-coordinate gives the row number (commonly starting from 0 at the top of the data).

image data
Data produced by scanning a surface with an optical or electronic device. Common examples include scanned documents, remotely sensed data (for example, satellite images), and aerial photographs. An image is stored as a raster dataset of binary or integer values that represent the intensity of reflected light, heat, or other range of values on the electromagnetic spectrum.

image division
A digital image processing technique for increasing the contrast between features in an image by dividing the pixel values in the image by the values of corresponding pixels in a second image. Image division is normally used to identify concentrations of vegetation.

image scale
The ratio between a distance in an image and the actual distance on the ground, calculated as focal length divided by the flying height above mean ground elevation. Image scale can vary in a single image from point to point due to surface relief and the tilt of the camera lens.

image server
A public ArcIMS virtual server for image services.

image service
In ArcIMS, a service that uses the spatial server image rendering capabilities. When a request is received, a map is generated on the server, and the response is sent back as a JPG, PNG, or GIF image. A new map image is generated each time a client requests new information.

image service definition
In ArcGIS Image Server, a workspace created using the Image Service Definition Editor toolbar that defines the key properties of a service, including name and default spatial reference system. The image service definition workspace has a .ISDef extension.

image service reference file
In ArcGIS Image Server, a file that stores properties for reestablishing a connection to a service and setting up user-defined image service properties. Image service reference files have a .ISRef extension.

image space
The x,y coordinate space defined by the number of columns and rows in a raster dataset. The origin of image space is commonly the center of the top left pixel of the data and is labeled (0,0). The x-axis corresponds to the number of columns in the raster, and the y-axis to the number of rows. For raster data to be used in GIS software, image space must be transformed to a real-world coordinate system through georeferencing.

imager
Any satellite or aerial instrument that measures and maps the earth and its atmosphere.

impedance
A measure of the amount of resistance, or cost, required to traverse a path in a network, or to move from one element in the network to another. Resistance may be a measure of travel distance, time, speed of travel multiplied by distance, and so on. Higher impedance values indicate more resistance to movement, and a value of zero indicates no resistance. An optimum path in a network is the path of lowest impedance, also called the least-cost path.

impedance model
In ArcInfo, a routing model that determines the best route by finding the path of least resistance.

impersonation
A process by which a Web application assumes the identity of a particular user and thus gains all the privileges to which that user is entitled.

implement
In programming an interface, to provide code for each of the methods of an interface (the interface is defined separately).

import
To bring data from one computer system or application into another. Importing often involves some form of data conversion.

inbound interface
An interface implemented by a class, on which a client can call members.

incident
In ArcGIS Network Analyst, a network location used in closest facility analysis. Car accidents, crime scenes, and fires are examples of incidents.

incident energy
Electromagnetic radiation that strikes a surface.

INCITS
Acronym for International Committee for Information Technology Standards. An ANSI-accredited forum that creates and maintains information and communications technology standards through the participation and consensus of its industry members.

independent variable
One or a set of variables used to model or predict the dependent variable. For example, a prediction of annual purchases for a proposed store (the dependent variable) might include independent variables representing the number of potential customers, distance to competition, store visibility, and local spending patterns. In the regression equation, independent variables appear on the right side of the equal sign and are often referred to as explanatory variable.

indeterminate flow direction
In networks, a flow direction that is unknown or undiscoverable. Indeterminate flow direction occurs when flow direction cannot be determined from the connectivity of the network, the locations of sources and sinks, and the enabled or disabled states of features.

index
A data structure, usually an array, used to speed the search for records in a database or for spatial features in geographic datasets. In general, unique identifiers stored in a key field point to records or files holding more detailed information.

index contour line
On a topographic map, a contour line that is thicker than the rest and usually labeled with the elevation that it represents. Depending on the contour interval, every fourth or fifth contour line may be an index contour.

index map
A schematic map used as a reference for a collection of map sheets, outlining the total area covered along with the coverage extent of, and usually a name or reference for, each map sheet.

industry
An organization with specific GIS needs. Examples of industries include government, transportation, health care, homeland security, and public safety.

INFO database
A tabular database management system used by ArcInfo Workstation software to store and manipulate attributes of a GIS dataset in ArcInfo Workstation format. INFO databases are stored inside a workspace folder with subdirectories containing files that represent the geometry and topology that make up a coverage.

information space
A geometric representation of relationships between elements in a data domain, in which relative position indicates the degree of similarity between elements. Information spaces are often based on geographic metaphors and are used to provide more intuitive views of a complex, multidimensional data domain.

Informix
A commercial relational database management system (RDBMS) supported by ArcSDE.

infrared scanner
A device that detects infrared radiation and converts it into an electrical signal that can be recorded on film or magnetic tape.

infrastructure
The system of human-made physical structures, such as roads, bridges, canals, cables, wires, communications towers, hospitals, pipes, reservoirs, and sewers, that provide communication, transportation, public services, utilities, or all of the above to a populace.

inheritance
In object-oriented programming, the acquisition of methods and properties by child classes or interfaces from their previously existing parent classes or interfaces. Inheritance is one of the defining characteristics of an object-oriented system.

in-process
Within the process space of a client application, a class contained in a DLL is in-process, as objects are loaded into the process space of the client EXE. A component contained in a separate EXE is out-of-process.

input data
Data that is entered into a computer, device, program, or process.

input event record
In geocoding, a piece of information such as a customer address and location of an incident. Input event record types vary by application. They include customer addresses, location of the event or incident, location of equipment and facilities, and the monument offset.

input feature
In geoprocessing, data put into the system for processing, usually specified by a path in a dialog box, script, or at the command line.

input table
In geoprocessing, tabular data put into the system for processing, usually specified by a path in a dialog box, script, or at the command line.

inset map
A small map set within a larger map. An inset map might show a detailed part of the map at a larger scale, or the extent of the existing map drawn at a smaller scale within the context of a larger area.

instance
In object-oriented programming, a single object created based on the template or definition of the class to which it belongs.

instantiation
In programming, the process of creating a single object based on the template or definition of the class to which it belongs.

instrument setup field
In the Survey Analyst for field measurements Survey Explorer, a field that allows the user to select the instrument setup or enter the name of a new instrument setup.

integer data
Data that represents phenomena with distinct boundaries. Property lines and streets are examples of discrete data.

integrated development environment
A software development tool for creating applications, such as desktop and Web applications. IDEs blend user interface design and layout tools with coding and debugging tools.

integrated feature dataset
In geodatabases, a feature dataset that stores topologically associated feature classes. The topological editing tools in ArcMap can be used to maintain the topological associations of features in an integrated feature dataset. Network feature classes do not participate in the topological associations within an integrated feature dataset.

integration
A high degree of interconnection between two or more programs or datasets, in which they share a common schema, ontology, semantic approach, or method that allows information to be passed between them without being fully processed.

intensity
In the IHS (intensity, hue, saturation) color model, the relative brightness of a color.

interactive vectorization
A manual process for converting raster data into vector features that involves tracing raster cells.

interchange format
A file format that allows the easy exchange of data between different software programs.

Interface Definition Language
A language used to define COM interfaces. The Microsoft implementation of IDL may also be referred to as MIDL or Microsoft IDL.

interferogram
A radar image that records interference patterns captured by two antennae a short distance apart.

interior feature weight
One of two weights that allow control of how labels are placed relative to polygon features in ArcMap. Higher feature weights prevent labels from being placed over features. A high interior weight prevent labels from occupying the interior of polygon features.

intermediate data
Any data in a process that did not exist before the process existed and that will not be maintained after the process executes.

international date line
An imaginary line, generally following the meridian of longitude lying 180 degrees east and west of the Greenwich meridian, where the date changes. The time zone east of the international date line is twelve hours ahead of Greenwich mean time; the time zone west of the international date line is twelve hours behind Greenwich mean time. A traveler going west across the date line adds a day; a traveler going east across it subtracts a day.

international meridian
The meridian adopted by international agreement in 1884 as the prime meridian, the 0-degree meridian from which all other longitudes are calculated. The Greenwich prime meridian runs through the Royal Observatory in Greenwich, England.

International Organization for Standardization
A federation of national standards institutes from 145 countries that works with international organizations, governments, industries, businesses, and consumer representatives to define and maintain criteria for international standards.

internationalization
The process of creating software that can be adapted to the requirements of different languages and cultures without substantive changes to the source code.

Internet
The global network of computers that communicate through common protocols, such as TCP/IP.

interoperability
The capability of components or systems to exchange data with other components or systems, or to perform in multiple environments. In GIS, interoperability is required for a GIS user using software from one vendor to study data compiled with GIS software from a different provider.

interpolation
The estimation of surface values at unsampled points based on known surface values of surrounding points. Interpolation can be used to estimate elevation, rainfall, temperature, chemical dispersion, or other spatially-based phenomena. Interpolation is commonly a raster operation, but it can also be done in a vector environment using a TIN surface model. There are several well-known interpolation techniques, including spline and kriging.

interrupted projection
A world projection that reduces distortion by dividing the projected area into gores, each with its own central meridian.

intersect
A geometric integration of spatial datasets that preserves features or portions of features that fall within areas common to all input datasets.

intersection
The point where two lines cross. In geocoding, most often a street crossing.

intersection connector
A character used in address data to indicate that an address is located at an intersection. For example, in the address "S. Huntington Dr. &amp; E. Clark Blvd." the ampersand (&amp;) character is the intersection connector. The intersection connector delimits the address into two parts and assigns intersection searches to the address.

intranet
A computer network, often using the same software and serving the same functions as those found on the Internet, that is restricted to users within an organization.

intrinsic stationarity
In spatial statistics, the assumption that a set of data comes from a random process with a constant mean and a semivariogram that depends only on the distance and direction separating any two locations.

inverse distance
One divided by distance, often raised to some power (1/D or 1/D2, for example), where D is a distance value. By inverting the distance among spatial features, and using that inverted value as a weight, near things have a larger weight or influence than things that are farther away.

inverse distance weighted interpolation
An interpolation technique that estimates cell values in a raster from a set of sample points that have been weighted so that the farther a sampled point is from the cell being evaluated, the less weight it has in the calculation of the cell's value.

IP address
Acronym for Internet protocol address. A unique number, such as 10.48.6.8, that identifies each computer on the Internet. IP addresses are similar to phone numbers, and allow data to travel between one computer and another via the Internet.

irregular triangular mesh
A vector data structure that partitions geographic space into contiguous, nonoverlapping triangles. The vertices of each triangle are sample data points with x-, y-, and z-values. These sample points are connected by lines to form Delaunay triangles. TINs are used to store and display surface models.

irregular triangular surface model
A vector data structure that partitions geographic space into contiguous, nonoverlapping triangles. The vertices of each triangle are sample data points with x-, y-, and z-values. These sample points are connected by lines to form Delaunay triangles. TINs are used to store and display surface models.

isanomal
A line on a map connecting points of equal difference from a normal value, usually a meteorological value such as average temperature.

isarithm
An isoline drawn according to values that can occur at points; an isometric line.

ISO
Abbreviation for International Organization for Standardization</I>. A federation of national standards institutes from 145 countries that works with international organizations, governments, industries, businesses, and consumer representatives to define and maintain criteria for international standards.

isobar
A line on a weather map connecting places of equal barometric pressure.

isochrone
A line on a map connecting points of equal elapsed time; especially, travel time to or from a given location.

isohyet
A line on a map connecting points of equal rainfall.

isolation level
A setting in a database management system (DBMS) that defines how much an application process is isolated from other concurrently executing processes in a DBMS. It specifies the degree to which the rows read and updated by the application are available to other concurrently executing processes. It also specifies the degree to which updates from other concurrently executing application processes are available to the application.

isoline
A line connecting points of equal value on a map. Isolines fall into two classes: those in which the values actually exist at points, such as temperature or elevation values, and those in which the values are ratios that exist over areas, such as population per square kilometer or crop yield per acre. The first type of isoline is specifically called an isometric line or isarithm; the second type is called an isopleth.

isometric line
An isoline drawn according to known values, either sampled or derived, that can occur at points. Examples of sampled quantities that can occur at points are elevation above sea level, an actual temperature, or an actual depth of precipitation. Examples of derived values that can occur at points are the average of temperature over time for one point or the ratio of smoggy days to clear days for one point.

isopleth
An isoline drawn according to known values that can only be recorded for areas, not points. Examples include population per square mile or the ratio of residential land to total land for an area.

isotherm
A line on a map connecting points of equal temperature.

isotropic
Having uniform spatial distribution of movement or properties, usually across a surface.

isotropy
A property of a natural process or data where spatial dependence (autocorrelation) changes only with the distance between two locations&#8212;direction is unimportant.

item
An element in the Catalog tree. Items include data sources, such as shapefiles and geodatabases, and nonspatial elements, such as folders.

iterative procedure
A repetitive or recurring procedure.

IUnknown
All COM interfaces inherit from the IUnknown interface. The default implementation of IUnknown controls object lifetime and provides runtime type support.