South Central Arc User Group

Established 1990

GIS Glossary

The field of Geographic Information Systems (GIS) is filled with scientific terminology that can become very frustrating to those attempting to learn about it. Below are some definitions that will help you understand the information presented in this site. Below the definitions are several links to other GIS dictionaries for further GIS terms.

GIS Glossary

Accuracy - "The closeness of observations, computations or estimates to the true value as accepted as being true. Accuracy relates to the exactness of the result, and is distinguished from precision which relates to the exactness of the operation by which the result was obtained" (Gittings & Patterson, 1999).

Address - "1. A means of referencing an object for the purposes of unique identification and location. 2. The location of a block of computer memory" (Gittings & Patterson, 1999).

Attribute - "1. Descriptive information characterizing a geographical feature (point, line, area). 2. Commonly, a fact describing an entity in a relational model, equivalent to the column in a relational table" (Bonham-Carter, 1994, p. 348).

Cadastre - "A public register or survey that defines or reestablishes boundaries of public and/or private land for purposes of ownership and/or taxation" (Bonham-Carter, 1994, p. 351).

Cartography - "The organization and communication of geographically related information in either graphic or digital form. It can include all stages from data acquisition to presentation and use" (Gittings & Patterson, 1999).

Centerline - "1. A line digitized along the center of a linear feature. 2. A line drawn from the center point of a vertical aerial photograph through the transposed center point of an overlapping aerial photograph" (Gittings & Patterson, 1999).

Coordinate system - "A reference system for the unique definition of a location of a point in n-dimensional space" (Bonham-Carter, 1994, p. 355).

Coverage - "1. An object in a spatial data base. The representation of a map composed of graphic and attribute files in a digital mapping system. 2. In remote sensing, often used to describe the extent of the Earth's surface represented on an image or a set of images, as in aerial coverage" (Bonham-Carter, 1994, p. 355).

Data model - "Collection of concepts allowing for the representation of an environment according to arbitrary requirements" (Bonham-Carter, 1994, p. 356).

Datum - "1. Any point, line, or surface used as a reference for a measurement of another quantity. 2. A model of the earth used for geodetic calculations" (Bonham-Carter, 1994, p. 356).

Feature - "An object in a spatial data base with a distinct set of characteristics" (Bonham-Carter, 1994, p. 359).

Geocoding - "1. Synonym for 'address coding'. 2. Process of assigning geographic locations to objects" (Bonham-Carter, 1994, p. 360).

Geodetic reference system - "The true technical name for a datum. The combination of an ellipsoid, which specifies the size and shape of the earth, and a base point from which the latitude and longitude of all other points are referenced" (GIS Development, n.d.).

Geographic database - "A collection of spatial data and related descriptive data organized for efficient storage and retrieval by many users" (GIS Development, n.d.).

Georeference - "To establish the relationship between page coordinates on a planar map and known real-world coordinates" (Gittings & Patterson, 1999).

"Heads-up" digitizing - "A digitizing station that provides a graphical user interface on the screen of a workstation (hence sometimes called on-screen digitizing). The operator uses a pointing device (mouse or trackball) to navigate on the scanned image of the original source, without having to look down at a digitizing tablet" (Chrisman, 1997, p. 71).

Map projection - "A method of representing the earth's three-dimensional surface as a flat two-dimensional surface. This normally involves a mathematical model that transforms the locations of features on the earth's surface to locations on a two-dimensional surface. Because the earth is three-dimensional, some method must be used to depict the map in two dimensions. Therefore such representations distort some parameter of the earth's surface, be it distance, area, shape, or direction" (Gittings & Patterson, 1999).

Metadata - "Data about data and usage aspects of it" (Gittings & Patterson, 1999).

Open GIS Consortium (OGC) - "The Open GIS Consortium is a voluntary, non-governmental, nonprofit organization dedicated to the development of an open systems approach to geoprocessing. The OGC was initiated in August 1994 by the Open Systems Foundation (OSF) to spearhead the Open GeoData Interoperability Specification (OGIS) project" (Gittings & Patterson, 1999).

Open systems - "An information processing system that complies with the requirements of open systems interconnection (OSI) standards in communication with other such systems" (Gittings & Patterson, 1999).

Open Systems Interconnection (OSI) - "This defines the accepted international standard by which open systems should communicate with each other. It takes the form of a seven-layer model of a network architecture, with each layer performing a different function" (Gittings & Patterson, 1999).

Orthophotograph - "A photographic copy of a perspective photograph with distortions due to tilt and relief removed" (Bonham-Carter, 1994, p. 370).

Photogrammetry - "The art and science of obtaining reliable measurements through use of photographs" (Bonham-Carter, 1994, p. 371).

Raster - "1. An element of a space that has been subdivided into regular tiles by tessellation. 2. Commonly, a data set, as for an image or DEM, composed of rasters. 3. Often used as a synonym for grid" (Bonham-Carter, 1994, p. 373).

Remote sensing - "1. Acquisition of information about the properties of an object or phenomenon using a recording device that is not in physical contact with the object of the study. 2. Commonly, information gathered using airborne or satellite platforms" (Bonham-Carter, 1994, p. 374).

Resolution - "A measure of the ability to detect quantities. High resolution implies a high degree of discrimination but has no implication as to accuracy" (Gittings & Patterson, 1999).

Shapefile - "An ArcView GIS data set used to represent a set of geographic features such as streets, hospital locations, trade areas, and ZIP Code boundaries. Shapefiles can represent point, line, or area features. Each feature in a shapefile represents a single geographic feature and its attributes" (Environmental Systems Research Institute, Inc. [ESRI], 1998, p. 27).

Spatial data - "Any information about the location and shape of, and relationships among, geographic features. This includes remotely sensed data as well as map data" (Gittings & Patterson, 1999).

Vector - "1. A quantity which has magnitude and direction. 2. Commonly, the notation used to represent spatial information" (Bonham-Carter, 1994, p. 381).


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