GIS Tasks

General purpose GISs essentially perform six processes or tasks.

• Input
• Manipulation
• Management
• Query
• Analysis
• Visualization

Input
Before geographic data can be used in a GIS it must be converted into a suitable digital format. The process of converting data from analogue paper maps into computer files is called digitizing. Modern GIS technology has the capability to automate this process fully for large projects; smaller jobs may require some manual digitizing.

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 your system. For example, geographic information is available at different scales (street centerline files might be available at a scale of 1:100,000; postal codes at 1:10,000; and census boundaries at 1:50,000). Before these can be overlaid and integrated they must be transformed to the same scale. This could be a temporary transformation for display purposes or a permanent one required for analysis. There are many other examples of data manipulation that are routinely performed in GIS. These include projection changes, data aggregation (for example, to convert sales territories for census building blocks), and generalization (weeding out unnecessary data).

Management
For small GIS projects it may be sufficient to store geographic information as computer files. There comes a point, however, when data volumes become large and the number of users of the data becomes more than a few, that it is best to use a database management system (DBMS) to help store, organize, and manage data. A DBMS is nothing more than computer software to manage a database–an integrated collection of data.

There are many different designs of DBMS, but in GIS the relational design has found most favor. In the relational design, data are stored conceptually as a collection of tables. Common fields in different tables are used to link them together. This surprisingly simple design has been so widely used mainly because of its flexibility and very wide deployment in applications both within and without GIS.

Query
Once you have a functioning GIS containing your geographic information, you can begin to ask questions such as:

• Where are all the sites suitable for building new houses?
• What is the dominant soil type for oak forest?
• If I build a new highway here how will traffic be affected?

Both simple and sophisticated queries utilizing more than one data layer can provide timely information to analysts and managers alike.

Analysis
GIS systems really come into their own when they are used to analyze geographic data. The processes of geographic analysis (often called spatial analysis or geoprocessing) uses the geographic properties of features to look for patterns and trends, and to undertake “what if” scenarios. Modern GISs have many powerful analytical tools, but two are especially important.

Proximity Analysis
GISs are often used to answer such questions as

• How many houses lie within 100 m of this water main?
• What is the total number of customers within 10 km of this store?
• What proportion of the alfalfa crop is within 500 m of the well?

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, or land ownership with tax assessment.

Visualization
For many types of geographic operation the end result is best visualized 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.