Geographical Information System (GIS)

A GIS is a computer system capable of assembling, storing, manipulating and displaying geographically referenced information, i.e. data identified according to their locations. GIS suffers from a universally accepted definition and the definitions include land information system (LIS), Land and resource information system (LRIS), Urban information system (URIS), and Environmental information system (ERIS) and Cadastral information system (CAIS).

Important characteristics of GIS

GIS advances as powerful tools for integrating data from different sources, The vocabulary of GIS overlaps that of computer science and mathematics in general, and computer applications in particular, The four MS : Measurement (measure environmental parameters), Mapping (develop maps which portray characteristics of the earth), Monitoring (monitor changes in our surroundings in space and time), and Modeling (model alternative actions and processes in the environment) can be enhanced through the use of a GIS, GIS is both data base information system and a higher order map, Any tabular data including census and hydrogeologic data can be converted to map-like form in a GIS, GIS is a computerized map making.

Components of GIS

A geographical information system has the components- computer hardware, software, geographic data, skilled people, and display layers of spatial data.

Computer Hardware

The computer has a hard disk drive for storing data and programs but extra storage can be done by a net work, digital tape cassettes, optical CD-ROMs etc. A digitizer as scanner is used to convert maps and documents into digital form and that can be used by the computer programs. A plotter or printer is used to present the results of the data processing.

Software

The five functional groups for a GIS software and these are data input and verification, data storage and database management, data output and presentation, data transformation and interaction with the user (Burrough, 1998). Software helps in storage, analysis, and display geographic information.

Data

Data is one of the important components of GIS and it may primary or secondary. A GIS integrates spatial data with other data and can even use as a data base management system (DBMS).
(i) General Reference Maps: World, country and state, district and village maps,
(ii) Base Maps- Include boundaries of rivers and lake, parks and landmarks, place names, street and highways and raster maps,
(iii) Demographic data includes data on general population, age, education employment, and households, housing units, income by family and households,
(iv) Physical data includes data on flood plain, land use, municipal data base and road business maps and data includes data on consumer,
(v) Environmental map and data: Include data related to the environment, weather elements, satellite imagery, topography, and natural resources, and
(vi) Business Maps and data: Includes data on consumer products, real estate, telecommunications, and commercial business establishments, financial services and transportation networks.

Skilled people

Technical specialists are needed for the effective working of GIS. The GIS technology is meaningless without the skilled people who can well manage the GIS technology.
Display layers of spatial data
All of the information would be layered and displayed with each type of information being represented in a different colour. The colour allows user to easily distinguish between different types of data information from any of the data bases can be overlaid on one map. A GIS can combine many map types and display them in three-dimensional perspective views that convey information more effectively than two dimensional maps.

Working of GIS

The working of a GIS includes six stages and these include
(i) Relating information from different sources,
(ii) Data capture,
(iii) Data integration,
(iv) Projection and registration,
(v) Data structure, and
(vi) Data modeling.

Relating information from different sources

A GIS relates information from different sources in the form of thematic layers and the primary requirement for the source data is that locations which may be annotated by X, Y and Z coordinates of longitude, latitude, and elevation or national grid coordinates.

A vector model

Here information on points, lines and polygons are represented and stored as a collection of X, Y coordinates. A point feature like an observation well can be represented by a single X and Y coordinate, a linear features like roads and drainages, a collection of point co-ordinates of X and Y and Polygonal features such as sub-basins of a river basin (e.g. in the present study four order sub-basins) as a closed loop of X and Y coordinates. The vector models are useful for describing discrete features and vector data files can approximate the appearance of hand drafted maps.

A raster model

It is a collection of grid cells like a scanned map or picture. Like vector model raster model is also used for storing geographic data. Raster data files can be manipulated quickly by the computer but less detailed and less visually appealing than vector data files.

Data capture

Data capture is the process of putting the information into the GIS system and is a time consuming component of GIS work. A GIS can use an information only that in digital form, in a form the computer can recognize. Thus maps can be digitized, or hand traced with at computer mouse, to collect coordinates of features. Electronic scanning devices are also used to convert map lines and points to digits.

Editing of information is very difficult. Electronic scanner records blemishes on maps as faithfully as they record the map features. A fleck of dirt connecting two lines should not be connected. The extraneous data to be edited or removed from the digital data. Editing of information is also a time consuming one. During the process of segment checking, dead and correction, self-overlap and intersections of segments are also to be removed and this needs patience of the skilled person involved is also necessary. In the present study, the land use / land cover map editing took days for dead end, self overlap and intersection corrections.

Data Integration

A GIS can line or integrate information difficult to associate through other means. Thus we can say that a GIS can use combinations of mapped variables to build and analyze new variable.

Projection and registration

The fourth phase of a GIS work is projection and registration. A digital data can be analysed only if the data may have undergone projection, and thus integrate them (digital) data into a GIS. Projection is a basis component of cartography and is a mathematical means of transferring information from the earth’s three-dimensional curved surface to a two dimensional medium paper or computer screen. Different projections are utilized for different types of maps because each projection is particularly appropriate to certain uses.

Data structure

A GIS has the ability to convert data from one structure to another. That is from raster data file (Raster data file consists of row of uniform cells coded according to data values) to vector data file. For example, during data restructuring, a GIS can convert a satellite image map to a vector structure by generating lines around all cells.

Data Modeling

A GIS can represent two and three dimensional characteristics of the earth’s surface, sub-surface and atmosphere from information points in the form of maps. A GIS can very quickly generate maps with lines, for example if GIS makes a map from rainfall amounts, such a map may be a rainfall contour map. A contour map created from surface modeling of rainfall point measurements may be overlained and analyzed with little difficulty with any other map in a GIS covering the same area.

2.3 Applications of GIS

The important applications of GIS include
a. Disaster monitoring,
b. Sea level monitoring,
c. In the field of defence ways to win war
d. Land Use category changes, crop rotation and their impact in environment,
e. Impact analysis. For example, impact of Methyl Iso Cyanate (MIC) released from Union Carbide during Bhopal tragedy,
f. Study the spread of diseases,
g. Selection of gardens,
h. Map making,
i. Emergency response planning,
j. Simulating environmental effects.

2.4 GIS in India

When we compare the development of GIS techniques in India with that of other developed and developing countries, it has not gained any momentum. In India GIS is still in infant stage. The basic reasons may include difficulty to develop software and hardware, lack of well trained persons, won’t get reliable data on many places, for example Lakshadweep and most of the R&D institutions rare hesitant to provide data.