Modeling is a powerful and flexible analysis tool. Modeling is the process of creating new layers from combining or operating upon existing layers. Use modeling to create a small set of layers—perhaps even a single layer—which, at a glance, contains many types of information about the study area.
For example, if you want to find the best areas for a bird sanctuary, taking into account vegetation, availability of water, climate, and distance from highly developed areas, you would create a thematic layer for each of these criteria. Then, each of these layers would be input to a model. The modeling process would create one thematic layer, showing only the best areas for the sanctuary.
The set of procedures that define the criteria is called a model. In ERDAS IMAGINE, models can be created graphically and resemble a flow chart of steps, or they can be created using a script language. Although these two types of models look different, they are essentially the same—input files are defined, functions and operators are specified, and outputs are defined. The model is run and a new output layer or layers are created. Models can utilize analysis functions that have been previously defined, or new functions can be created by you.
Use Spatial Modeler to create graphical models and SML to create script models.
In modeling, the concept of layers is especially important. Before computers were used for modeling, the most widely used approach was to overlay registered maps on paper or transparencies, with each map corresponding to a separate theme. Today, digital files replace these hardcopy layers and allow much more flexibility for recoloring, recoding, and reproducing geographical information (Steinitz et al, 1976).
In a model, the corresponding pixels at the same coordinates in all input layers are addressed as if they were physically overlaid like hard-copy maps.