The modelling capability of GIS makes use of the processing power of a computer to attempt to predict the outcome of a proposed scenario.

In any decision making or planning procedure it is beneficial to predict the outcome of the action before the action is taken. For example, in deciding where to build a new highway the following question may be asked:

"Which route for the new highway has the lowest 'cost' in terms of loss of housing, prime agricultural land and forests, and minimizes the needs for cutting and filling?"