PRINCIPLES OF GEOGRAPHIC INFORMATION SYSTEM (GIS)

PRINCIPLES OF GEOGRAPHIC INFORMATION SYSTEM (GIS) TECHNOLOGY

                Apart from the computing machine itself, another tool that is central to geospatial information technology is the Geographic Information System (GIS). In this sense, GIS can be regarded as a subset of GIT.

                Geographic Information System (GIS) is a computerized information system for capturing, storing, integrating, manipulating, analyzing, checking and displaying data which are spatially referenced to the earth. It is capable of handling both positional and attribute data. GIS technology can be visualized as an integrated assemblage of computer hardware and software, spatially referenced data and human operator, it permits the  user to bring together information from numerous source in a composite form. The term GIS has been variously defined in surveying and cartographic literature. However, it is interesting to see the definition of the standard committee of U. K Association of Geographic Information (AGI). It defines GIS as “ A system for handling data which is directly indirectly referenced to the earth. It may be used for capturing, storing, validating, manipulating, analyzing, displaying, or managing such data. It is normally considered to involve spatially referenced computer data base appropriate software. A primary function of a GIS is its ability to integrate data from a variety of sources. Of interest too,. is the simple and concise definition given by fisher and Lindernberg. They defined GIS as “ The management, analysis and manipulation of spatially referenced information in a problem solving synthesis.

                The development of GIS started several years ago. Since then, there has been a tremendous expansion of activities in this area as a result of development in electronics and computer technology as well as increased user needs. Today , it is a new scientific emphasis for a variety of professionals.

                At times, people erroneously consider Land Information System LIS to be synonymous with GIS, especially those who are not In the general area of surveying and mapping. There is a fine line of demarcation. We have seen the definition of GIS by AGI above, let us take a look at the definition of LIS by the international Federation of Surveyors. This International body defines LIS as a tool for legal and administrative and economic decision making and an aid for planning and development which consist, on one hand, of a database containing spatially referenced data for a defined area and on the other hand, of procedures and techniques for the systematic collection, updating, processing, and distribution of the data. The base of an LIS is a uniform spatial referencing system for the data in the system which also facilitates the linking of data within the system to the other land related data.

                As can be seen from the above definition, formation of database is a common denominator for LIS and GIS. Both systems include a database to store both graphic and attribute data about individual features or areas present in the landscape; database management system (DBMS) ; and the requisite software or tools to analyse the data held in the system. Systems, which are designed for or applied primarily to small scale, mainly area-based, thematic data are usually termed Geographic Information System (GIS). The term Land information System (LIS) tends to be associated with those systems which are based on the more detailed and more accurately surveyed point and line information required for cadastral and administrative purposes or for support and management of the facilities provided by public utilities. So, the difference lies mainly in the database content and overall application.

                The geographic information field is attracting professional  from many disciplines. As a computerized system for the collection, storage, retrieval and presentation of spatially referenced data, GIS is becoming a tool for every profession dealing with spatially referenced data.

                OPERATIONAL PRINCIPLES

                A typical geographic information system has three(3) processing steps or subsystems consisting of:

1.       Data Acquisition Subsystem

2.       Database Management Subsystem (DBMS)

3.       Data Presentation Subsystem.