Raster (Arithmetic) Overlay
Raster overlay superimposes at least two input raster layers to produce an output layer. Each cell in the output layer is calculated from the corresponding pixels in the input layers. To do this, the layers must line up perfectly; they must have the same pixel resolution and spatial extent. If they do not align, they can be adjusted to fit by the preprocessing functions discussed in Chapter 3. Once preprocessed, raster overlay is flexible, efficient, quick, and offers more overlay possibilities than vector overlay.