Definition of GIS

A GIS is basically a computerized information system like any other database, but with an important difference: all information in GIS must be linked to a geographic (spatial) reference (latitude/longitude, or other spatial coordinates).

There are many different definitions of GIS, as different users stress different aspects of its use. For example:

  1. ESRI defined GIS as an organized collection of computer hardware, software, geographic data and personnel designed to efficiently capture, store, update, manipulate, analyze and display geographically referenced information.
  2. ESRI also provided a simpler definition of GIS as a computer system capable of holding and using data describing places on the earth’s surface).
  3. Duecker defined GIS as 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 GIS manipulates data about these points, lines or areas to retrieve data for ad hoc queries and analyses.

The United States Geological Survey (USGS) defined provided A GIS as a computer hardware and software system designed to collect, manage, analyze and display geographically (spatially) referenced data. This definition is a fairly comprehensive and is suitable for agricultural applications of GIS

Note that a GIS does not store a map or image. What it stores is a relational database from which maps can be created as and when needed. Relational database concepts are particularly crucial to the development of GIS. Each map (say a soil map) can be considered to hold a layer or a level of information. A GIS works with several layers of such thematic data. It can answer questions by comparing the different layers and also by overlaying them if all the layers are referenced to the same locations, that is location is the common key for all the thematic data sets. This ensures that every location (spatial reference point) is exactly matched to its location on other maps. Once this is done, the different layers can be compared and analyzed singly and in combination to identify spatial patterns and processes. Thus, GIS are related to other database applications, but with an important difference; all information in a GIS must be linked to a spatial reference. Other data bases may contain locational information (addresses, pin codes etc), but the GIS uses georeferences as the primary means of storing and accessing information.