GIS is a computer-based software used for visualizing, manipulating, creating, analyzing and displaying the spatial data. Different definitions of a GIS have been evolved in different areas and disciplines (Clarke, 1995 and 2001; Burrough, 1986 and 1998; Duecker, 1979; Goodchild, 1992; and Star and Estes, 1990). According to Duecker (1979) geographic information system is a special case of information systems where the database consists of observations on spatially distributed features, activities or events, which are definable in space as points, lines, or areas. A geographic information system manipulates data about these points, lines, and areas to retrieve data for ad hoc queries and analyses.
Clarke (2001) considered GIS as a toolbox, as an information system, as an approach to science and as a multi-billion dollar business. The geographic imaging capabilities of a GIS have been enhanced tremendously with the support of image analysis, which includes data visualization, data extraction/creation, and data analysis. Arcview Image Analysis leverages a broad range of readily available image data types including popular satellite imagery, aerial photography, orthoimagery, and other remotely sensed data, which supplements a wide variety of GIS applications. The main advantages obtained from a GIS include data analysis, modeling and prediction. Thus, GIS is a powerful set of tools for storing and retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes (Burrough, 1986).
All definitions of GIS recognize that spatial data are unique because they are linked to maps. A GIS at least consists of a database, map information, and a computer-based link between them. GIS software lets the users to see, explore, and analyze data by location, revealing hidden patterns, relationships, and trends that are not readily apparent in spreadsheets or statistical packages.