A Geographic Information System (GIS) is a system for capturing,
storing, analyzing and managing data and associated attributes
which are spatially referenced to the earth. In the strictest
sense, it is a computer system capable of integrating, storing,
editing, analyzing, sharing, and displaying geographically-referenced
information. In a more generic sense, GIS is a tool that
allows users to create interactive queries (user created
searches), analyze the spatial information, edit data, maps,
and present the results of all these operations.
Data creation
Modern GIS technologies use digital information, for which
various digitized data creation methods are used. The most
common method of data creation is digitization, where a
hardcopy map or survey plan is transferred into a digital
medium through the use of a computer-aided drafting (CAD)
program, and georeferencing capabilities.
Data representation
GIS data represents real world objects (roads, land use,
elevation) with digital data. There are two broad methods
used to store data in a GIS for both abstractions: Raster
and Vector.
Projections, coordinate systems and registration
Map information in a GIS must be manipulated so that it
registers, or fits, with information gathered from other
maps. Before the digital data can be analyzed, they may
have to undergo other manipulations—projection and
coordinate conversions. The earth can be represented by
various models, each of which may provide a different set
of coordinates (e.g., latitude, longitude, elevation) for
any given point on the earth's surface. A projection is
a mathematical means of transferring information from a
model of the Earth, which represents a three-dimensional
curved surface, to a two-dimensional medium—paper
or a computer screen.
