GEOGRAPHIC

 INFORMATION SYSTEM (GIS)           

GIS tasks

General-purpose geographic information systems essentially perform six processes or tasks:

Input
Before geographic data can be used in a GIS, the data must be converted into a suitable digital format. The process of converting data from paper maps into computer files is called digitising. Modern GIS technology can automate this process fully for large projects using scanning technology; smaller jobs may require some manual digitising (using a digitising table). Today many types of geographic data already exist in GIS-compatible formats. These data can be obtained from data suppliers and loaded directly into a GIS.

Manipulation
It is likely that data types required for a particular GIS project will need to be transformed or manipulated in some way to make them compatible with user's system. For example, geographic information is available at different scales (detailed street centreline files; less detailed census boundaries; and postal codes at a regional level). Before this information can be integrated, it must be transformed to the same scale (degree of detail or accuracy). This could be a temporary transformation for display purposes or a permanent one required for analysis. GIS technology offers many tools for manipulating spatial data and for weeding out unnecessary data.

Management

For small GIS projects, it may be sufficient to store geographic information as simple files. However, when data volumes become large and the number of data users becomes more than a few, it is often best to use a database management system (DBMS) to help store, organise, and manage data. DBMS is nothing more than computer software for managing a database.

There are many different designs of DBMS’s, but in GIS the relational design has been the most useful. In the relational design, data are stored conceptually as a collection of tables. Common fields in different tables are linked together. This surprisingly simple design has been so widely used primarily because of its flexibility, with very wide deployment in applications both within and without GIS.

Query and Analysis

Once the geographic information/data is entered in to GIS, simple queries such as ownership of the land parcel, distance between two places, zoning for industrial use, and analytical questions such as, location of sites suitable for building new houses, dominant vegetation and soil types in western ghats, traffic control by ring roads, flyover and sub urban transit system, can be done and results obtained quickly.

GIS provides both simple point-and-click query capabilities and sophisticated analysis tools to provide timely information to managers and analysts alike. GIS technology really comes into its own when used to analyse geographic data to look for patterns and trends and to undertake "what if" scenarios.

Proximity Analysis

This can be done to find out various elements within a desired distance from any object. The queries may be:

·         Number of plants / trees within 100 m of water source.

·         Total number of users within 10 km of a water source.

To answer such questions, GIS technology uses a process called buffering to determine the proximity relationship between features.

Overlay Analysis

The integration of different data layers involves a process called overlay. At its simplest, this could be a visual operation, but analytical operations require one or more data layers to be joined physically. This overlay, or spatial join, can integrate data on soils, slope, and vegetation.

Visualisation
For many types of geographic operation the end result is best visualised as a map or graph. Maps are very efficient at storing and communicating geographic information. While cartographers have created maps for millennia, GIS provides new and exciting tools to extend the art and science of cartography. Map displays can be integrated with reports, three-dimensional views, photographic images, and other output such as multimedia.

Data for GIS

The data to be acquired depends on how one wants to use map data and get output. Many project needs are met with the following common map data types.

Base maps: Include streets and highways; boundaries for census, postal, and political areas; rivers and lakes; parks and landmarks; place names; and USGS raster maps.

Business maps and data: Include data related to census/demography, consumer products, financial services, health care, real estate, telecommunications, emergency preparedness, crime, advertising, business establishments and transportation.

Environmental maps and data: Include data related to the environment, weather, environmental risk, satellite imagery, topography and natural resources.

General reference maps: World and country maps and data that can be a foundation for a database.

Advantages of GIS

The advantages of Geographic Information Systems (GIS) are:

·         Perform Geographic Queries and Analysis
The ability of GIS is to search databases and perform geographic queries through better analysis.

·         Improve Organisational Integration

GIS has the ability to link data sets together by geography, facilitating interdepartmental information sharing and communication. By creating a shared database, one department can benefit from the work of another - data can be collected once and used many times. GIS implemented organisations have achieved improved management of resources and improvement in organisational set-up.  With this, communication increases among individuals and departments. This has led to reduction in redundancy, enhanced productivity, and overall improvement in organisational efficiency.

·         Decision making

GIS technology has been used to assist in tasks such as presenting information at planning inquiries, helping resolve territorial disputes, and siting pylons in such a way as to minimise visual intrusion. A GIS, however, is not an automated decision making system but a tool to query, analyse, and map data in support of the decision making process. For example, GIS can be used to help reach a decision about the location of a new housing development that has minimal environmental impact, is located in a low-risk area, and is close to a population centre. The information can be presented succinctly and clearly in the form of a map and accompanying report, allowing decision makers to focus on the real issues rather than trying to understand the data. Because GIS products can be produced quickly, multiple scenarios can be evaluated efficiently and effectively.

·         Map making

The process of making maps with GIS is much more flexible than traditional manual or automated cartography approaches. It begins with database creation. Existing paper maps can be digitised and computer-compatible information can be translated into the GIS. The GIS-based cartographic database can be both continuous and scale free. Map products can then be created centred on any location, at any scale, showing selected information symbolised effectively to highlight specific characteristics.

The characteristics of atlas and map series can be encoded in computer programs and compared with the database at final production time. Digital products for use in other GISs can also be derived by simply copying data from the database. In a large organisation, topographic databases can be used as reference frameworks by other departments. In India, maps are prepared by the Survey of India (SOI). The conventions followed in map preparation by various agencies are explained below.