Geographical information system (GIS) is basically defined as a systematic integration of hardware and software for capturing, storing, displaying, updating manipulating and analyzing spatial data. GIS can also be viewed as an interdisciplinary area that incorporates many distinct fields of study such as:
1. Geodesy that is basically projection, surveying, cartography and so on. 2. Remote Sensing 3. Photogrammetry 4. Environmental Science 5. City Planning 6. Cognitive Science
As a result GIS relies on progress made in fields such as computer science, databases, statistics, and artificial intelligence. All the different problems and question that arises from the integration of multiple disciplines make a more than a simple tool.
Requirements for GIS –
Geographic Information requires a means of integration between different sources of data at different level of accuracy. System basically deals with the aspects of daily life, so it must be updated daily to keep it current and reliable. Much of the Information Stored in GIS are for practical use requires a special means of retrieval and manipulation.
GIS system and application basically deals with information that can be viewed as data with specific meaning and context rather than simple data.
Components of GIS system –
GIS system can be viewed as an integration of three components are hardware and software, data, people. Lets discuss them one by one:
- Hardware and software –
Hardware relates to device used by end users such as graphic devices or plotters and scanners. Data storage and manipulation is done using a range of processor. With the development of the Internet and Web based application, Web servers have become part of many system’s architecture, hence most GIS’s follows 3-Tier architecture.
Software parts relates to the processes used to define, store and manipulate the data and hence it is akin to DBMS. Different models are used to provide efficient means of storage retrieval and manipulation of data.
- Data –
Geographic data are basically divided into two main groups are vector and raster.
Vector data/layers in GIS refers to discrete objects represented by points, lines and polygons. Lines are formed by connecting two or more points and polygons are closed set of Lines. Layers represent geometries that share a common set of attributes. Objects within a layer have mutual topology. Vector sources include digitized maps, features extracted from image surveys and many more.
Raster data is a continuous grid of cells in two dimension or the equivalent of cubic cells in three dimension. Raster data are divided conceptually into categorical and continuous. In a categorical raster every cell value is linked to a category in a separate table.Examples Soil type, vegetation types.land suitability, and so on. Continuous raster images usually describes continuous phenomena in space such as Digital Elevation Model where each pixel is an elevation value. Unlike categorical raster, a continuous raster doesn’t have an attribute/category table attached. Typical Raster sources are aerial images, satellite images and scanned map images.
- People –
People are involved in all phases of development of a GIS system and in collecting data. They include cartographers and surveyors who create the maps and survey the land and the geographical features. They also include system users who collect the data, upload the data to system, manipulate the system and analyze the results.