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Geo Information System

  • 4. DEFINITIONS OF GIS

    The definitions of a GIS given by various authors are as follows

    1. “A spatial data handling system" (Marble et at, 1983).
    2. “A computer - assisted system for the capture, storage retrieval, analysis and display of spatial data, within a particular Organization" (Clarke, 1986).
    3. “A powerful set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world" (Burrough, 1987).
    4. “An internally referenced, automated, spatial information system" (Berry, 1986).
    5. "A system which uses a spatial data base to provide answers to queries of a geographical nature" (Goodchild, 1985).
    6. “A system for capturing, storing, checking, manipulating, analyzing and displaying data which are spatially referenced to the Earth” (DOE, 1987:132)
    7. “Any manual or computer based set of procedures used to store and manipulate geographically referenced data”( Aronoff, 1989:39)
    8. “An institutional entity, reflecting an organizational structure that integrates technology with a database, expertise and continuing financial support over time”(Carter, 1989:3)
    9. “An information technology which stores, analyses and display both spatial and non – spatial data”(Parker,1988:1547)
    10. “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 and areas to retrieve data for ad hoc queries and analyses”(Dueker,1979:106)
    11. “A database system in which most of the data are spatially indexed, and upon which a set of procedures operated in order to answer queries about spatial entities in the database”(Smith,1987:13)
    12. “An automated set of functions that provides professionals with advanced capabilities for the storage, retrieval, manipulation and display of geographically located data”(Ozemoy, Smith and Sicherman, 1981:92)
    13. “A powerful set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world”(Burrough, 1986:6)
    14. “A decision support system involving the integration of spatially referenced data in a problem solving environment”(Cowen, 1988:1554)
    15. “A system with advanced geo – modeling capabilities”(Koshkariov, Tikunov and Trofimov, 1989:259)
    16. “A form of MIS (Management Information System) that allows map display of the general information”(Devine and Field, 1986:18)

    Although the above definitions cover wide range of subjects and activities best refer to geographical information. Some times it is also termed as Spatial Information Systems as it deals with located data, for objects positioned in any space, not just geographical, a term for world space. Similarly, the term 'a spatial data' is often used as a synonym for attribute data (i.e. rainfall / temperature / soil chemical parameters / population data etc are referred as attribute data).

    GIS Terminology

    Some of the terms used in GIS are briefly explained below:

    Data Planes, are discrete sets of data. For example, an imagery, a thematic map, a topographic sheet, a page of survey data each constitutes a data plane.

    Themes, are maps containing different types of information. For example, a toposheet contains contours, roads, railways, boundaries of forests etc. Each of these constitutes a theme.

    Registration, the themes in a given data plane are spatially related to each other. We say that the data is registered. Data in different planes may not be so readily related. Scales may vary, there may be transitional and rotational errors. This process of correction and development of an invariant spatial relationship between different data planes is called registration.

    Database, the spatially registered set of data constitutes a spatial database. In addition, each spatial object has an associated attribute. This could be a name, a number, a range of values etc. For example, a contour has a number, a road has a name. Such attributes also form a part of the database. Further, there may be other data sets associated demographic data.

    Spatial objects, all spatial objects can be represented by points, lines and polygons. A city is a point, a road is a line and a forest area is a polygon. The manners in which these fundamental units are represented are defined by the spatial data model. For example, we can have a chain as a set of line segments, a closed chain forms a polygon, an open chain is a line, a line segment of zero length is a point.

    Scale, this is the relationship between distances on the ground and distances on a map. Scale always applies to linear measures, never to area or elevations.

    Resolutions, this is the smallest element which can be distinguished in a data set. In case of imagery, this usually is the pixel size or a multiple to the pixel size. However, in a map this term can be confusing. This may be taken to mean the smallest mappable feature. However, some features are mapped by symbols even if their size is small.