ABSTRACT
There are many different types of model. Jeffers [6] provides a taxonomy of models used in environmental modeling, including matrix, stochastic, multivariate, optimization, topological, and dynamic. Some models are well known in different areas of environmental science, for example, the state-factor model of soil formation [7], neutral model in landscape ecology [8], and process models such as CENTURY [9-11]. Other modeling approaches representing some of the families of models described by Jeffers are also well known in GIS, including kriging, statistical and spatial-statistical models, agent-based models, and cellular automota. Other analytical approaches exploit terrain geometry to estimate topographically related variables or estimates of enviromental condition [12]. These range from relatively simple derivative variables such as slope gradient and aspect [13], or fl ow accumulation [14], to more complex properties such as soil moisture accumulation [15] or solar radiation input [16].
