"Good science starts with clear definitions. In the case of geographic information systems, however, definitions have sometimes been as clear as mud" (Clarke, 2001, p. 2). Nevertheless, Clarke (2001) has discussed five definitions of GIS.

First, a GIS is a toolbox or process. GIS can be viewed as a set of tools for analyzing spatial data, "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" (Burrogh, 1986, p. 6), and a set of "automated systems for the capture, storage, retrieval, analysis, and display of spatial data" (Clarke, 1995, p. 13).

Second, a GIS is an Information System. A GIS is a system for delivering answers to questions or queries; "an information system that is designed to work with data referenced by spatial or geographic coordinates. "In other words, a GIS is both a database system with specific capabilities for spatially-referenced data, and a set of operations for working with data" (Start and Estes, 1990, p. 2). Further, it is "a special case of information systems where databases 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" (Dueker, 1979, p. 106).

Third, GIS is an approach to science. "The generic issues that surround the use of GIS technology, impede its successful implementation, or emerge from an understanding of its potential capabilities" (Goodschild, 1992, p. 41).

Fourth, GIS are a multibillion-dollar industry. Groups monitoring the GIS industry estimate the total value of the hardware, software, and services conducted by the private, governmental, educational, and other sectors that handle spatial data to be billion of dollars a year (Clarke, 2001, p. 7).

Fifth, a GIS plays a role in society. A GIS is an "organized activity by which people measure and represent geographic phenomena and then transform these representations into other forms while interacting with social structures" (Chrisman, 1999, p. 175).