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5.33 Types of GIS

5.33.1 There are two major methods of storing mapped information: 1) Vector GIS and 2) Raster GIS. Geographic Information Systems which store map features in vector format store points, lines and polygons with high accuracy. They are preferred in urban applications where legal boundaries and the analysis of networks are important.

5.33.2 Raster GIS which stores map features in raster or grid format, generalize the location of features to a regular matrix of cells. Raster GIS data structures are preferred for digital elevation modeling, statistical analysis, remotely sensed data, simulation modeling and natural resource applications.
5.34 Thematic Mapping
5.34.1 Maps in Geographic Information Systems are represented thematically. A standard topographic map will show roads, rivers, contour elevations, vegetation, human settlement patterns and other features on a single map sheet. In a GIS these features are categorized separately and stored in different map themes or overlays. For example, roads will be stored in a separate overlay. Likewise, rivers and streams will each be stored as a separate theme. This way of organizing data in the GIS makes maps much more flexible to use since these themes can be combined in any manner that is useful. The following illustration shows conceptually how maps are stored as themes in a GIS. Each different theme is stored on a separate overlay. The vector based GIS, where the information is stored as a series of points, lines and polygons. The raster based GIS, where the information is stored as a series of discrete units called cells.
5.34.2 In addition to organising spatial data by themes mapped information is also structured as points, lines and ploygons. Besides the spatial information in a map, the GIS can usually store non-spatial information, which is related to the spatial entities. For instance an urban GIS database may have a map theme of property boundaries. Attached to each parcel will be a textual database, which might store the name of the owner, the address, the assessed value of the property, or the type of services and utilities on the site.

5.34.3 The GIS stores both spatial and non-spatial data in a database system which links the two types of data to provide flexible and powerful ways of querying or asking questions about the data.

5.34.4 Many Geographic Information Systems handle both vector and raster data from a wide variety of sources including satellite imagery, cadastral information, hand digitised maps and scanned images.
5.34.5 In order to ensure that all maps in a GIS database overlay accurately, the data set is 'geo-referenced' to a common coordinate system. In many countries the Universal Transverse Mercator (UTM) projection is commonly used to define coordinates in the GIS.
5.35 GIS Application
5.35.1 GIS application is dominant in land-use planning and management, mineral exploration, environmental impact studies, management of natural resources, natural hazard mapping, forestry and wildlife management, soil degradation studies, and enumeration area mapping. The applications of GIS is enormous of which the following fields derive great applications of a GIS system:

1. 
   Agricultural development
   
2. 
   Land evaluation analysis
   
3. 
   Change detection of vegetated areas
   
4. 
   Analysis of deforestation and associated environmental hazards
   
5. 
   Monitoring vegetation health
   
6. 
   Mapping percentage vegetation cover for the management of land Degradation
   
7. 
   Crop acreage and production estimation
   
8. 
   Wasteland mapping
   
9. 
   Soil resources mapping
   
10. 
    Groundwater potential mapping
    
11. 
    Geological and mineral exploration
    
12. 
    Snow-melt run-off forecasting
    
13. 
    Monitoring forest fire
    
14. 
    Monitoring ocean productivity etc.
    

5.36 Satellite Remote Sensing

5.36.1 Remote sensing connotes acquiring information about a phenomenon, object or surface while at a distance from it and without any physical contact with the objects, thus capture earth feature information from time to time, which is accurate, reliable and could be used for land related applications.

5.36.2 With respect to land resources, the satellite remote sensing has the applications namely: updating topo maps, Augmenting Databases, Image maps as base maps, Watershed management, Terrain evaluation, Road and infrastructure maps, Site suitability assessment, soil and crop suitability etc.
5.36.3 Further satellite imageries help monitoring the land use and land cover on a regular basis and help derive information on change detection and information on inaccessible areas. Different types of land classifications also be made by satellite imageries, for the productive and judicious use of land resources.
5.36.4 The present generation of satellites which capture high resolution images and has coordinate information, like Cartosat-I of India and Quickbird of the US. Other satellite data like Cartosat-II and Ikonos are also useful for land records. The cost of satellite data is much lower than the Ariel photographs, hence use of satellite data for land information system is a useful proposition.
Recommendations

1. 
   High Resolution Satellite Data preferably with one meter resolution and better should be used on continuous basis for building up time series data for Land Management.
   
2. 
   Archive Data on Land Use Land Cover and Geomorphology should be integrated with the High Resolution Satellite Data for identification of changes and classification purposes.
   
3. 
   Land suitability, irrigability, soil suitability, production estimates, crop/agriculture condition assessment etc could give value addition to the land parcel information for productive use by the farmers.
   
4. 
   For common property and other non-agriculture use, wasteland and land not suitable for agriculture could be identified by Satellite Imagery for judicious land use planning and economic gains for the Gram Panchayats.
   

5.37 Global Positioning System (GPS)
5.37.1 The Global Positioning System (GPS) is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations. It provides continuous three-dimensional positioning 24 hours a day throughout the world .The GPS technology has a tremendous amount of applications in GIS data collection, surveying, and mapping.
5.38 Components of GPS
5.38.1 The GPS technology is useful to the map makers and surveyors mainly for three purposes:

1. 
   To obtain accurate data up to about one hundred meters for navigation
   
2. 
   Meter level for mapping
   
3. 
   Millimetre level for geodetic positioning
   

5.38.2 The GPS is divided into three segments:

1. 
   Control Segment
   
2. 
   Space Segment
   
3. 
   User Segment