combining map data of similar dimension to produce new maps using algebraic operations

Map Algebra uses algebraic calculations to combine two or more maps of similar dimensions and output a new map based on these calculations. While primarily applied to raster data sets (GRID and image data), the same concepts can be applied to many types of cartographic information.

Map Algebra is organized into four major groups of operations – local, focal (or neighborhood), zonal, and incremental. Operators can be arithmetic, relational, or boolean.

GIS software contains many preset map algebra functions, allowing tasks to be performed without the user having to assemble them. Examples include slope calculation, creation of shaded relief from an elevation data set, or calculating a normalized difference vegetation Index (NDVI) using different bands from satellite imagery.

The vocabulary and conceptual framework for map algebra was developed through the 1980s by Professor C. Dana Tomlin as part of his PhD thesis work.