ABSTRACT

The types of models that we in the field of GIS, environmental modelling and engineering would be most interested in are those that express our understanding of the way the world works with sufficient precision and accuracy to allow prediction and confident decision-making. Such models may be qualitative, pictorial or more usually quantitative and relate to the dynamics and processes of the physical, social and economic environment. Many of these models of interest are used to explain and/or predict what happens somewhere. Since GIS are pre-eminent in handling spatial data, it is natural that efforts have been made to use or link such models with GIS in order to have an enhanced management tool. Typical examples of the types of models used include:

• regression lines predicting an output variable according to an input variable;

• spreadsheets expressing more complex interrelationships and processes; • manipulation of map layers according to a pre-determined theory; • a series of mathematical equations describing complex transport and

transformation processes compiled as a stand-alone computer pro­ gramme.