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geographic(al) information system

geographic(al) information system (GIS; geomatics (in Canada), geomatique (Francophone)) An information system for providing users with information about objects and features in their geographical contexts. A GIS allows users to display and analyze geographical relationships, and to investigate the effects of changes to the locations or characteristics of objects and features that are represented. The objects may be physical or administrative. Typical GIS applications are in Land Registry/Land Information Systems (LIS), in mapmaking, in land and resource management (e.g. by local authorities and utilities such as gas supply and distribution), and in market research, demographic studies, and environmental work.

A GIS typically consists of a special database management system (normally relational or object-oriented) that recognizes locational relationships, with closely integrated graphical input and output facilities, together with user facilities for manipulation and analysis of the objects and features in the database. The locational characteristics of objects and features may be recorded in vector form, i.e. in the form of coordinates in the real world (latitude and longitude, or some other grid system); alternatively the geographical region covered may be represented in raster form, i.e. as a regular (quasi-rectangular) pattern of cells in which objects are stored. Some systems provide integration of both forms of representation.

The objects in a GIS may represent points such as an individual mountain peak, lines such as a road or river, polygons such as a forest or the boundary of an administrative area, or continua such as elevation or climate. (Continua are commonly represented in a raster rather than a vector GIS.) The spatial data for a GIS may come from a variety of surveying techniques, including remote sensing imagery and global positioning systems, or from a postal address by geocoding (using existing data about the area covered by each zip code or postcode).

The database language includes facilities for locational queries (such as “how many hospitals are there in Hampshire?”) and locational responses (such as “where are the vineyards in California”), as well as statistical analyses.

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