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, organize, and manage data. A DBMS is nothing more than computer software for managing a database.

There are many different designs of DBMSs, 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 used to link them together. This surprisingly simple design has been so widely used primarily because of its flexibility and very wide deployment in applications both within and without GIS.

Query and Analysis

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

- Who owns the land parcel on the corner? - Where is land zoned for nature protection? - How far is it between two places?

or:

- How did land use change over a 60-year period?

And analytical questions such as

- What is the dominant soil type for oak forest? - Where are all the sites suitable for wind craft buildings? - If I build a new highway here, how will landscape be affected?

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 analyze geographic data 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

- How many houses lie within 200 m of this riverside? - What proportion of the alfalfa crop is within 500 m of the well? - What is the total number of customers within 10 km of this store?

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. Map displays can be integrated with reports, three-dimensional views, photographic images, and other output such as multimedia.