This applet demonstrates simple overlays of binary grids. Using Boolean logic concepts (common to many GIS) you can overlay using the three major functions: AND, OR and XOR (exclusive OR). IDRSI does not implement these Boolean functions as named; however you can perform the same actions using mathematical functions. While such functions (add, multiply, etc.) will work for any type of grid, they are typically most useful in binary overlays. Experiment with the IDRISI functions to see which ones emulate the Boolean ones.
Note that "ADD" can create on output grid with three classes. The "Reclass" button will reduce this to two.
How do I work this?