Map Algebra operators

You probably know more about Map Algebra operators than you think. Map Algebra operators are generally the same operators found on scientific calculators. The operators used most often (arithmetic, relational, Boolean, and logical) are also the simplest. Two less commonly used operators are combinatorial and bitwise.

Arithmetic operators allow addition, subtraction, multiplication, and division. For example, three rasters measuring three different types of fire risk could be added to create an overall risk analysis raster. Arithmetic operators can also be used to convert values from one measurement to another (e.g., feet x 0.3048 = meters).

Arithmetic operators.

Relational operators allow you to build logical tests, returning values of true (1) and false (0). For example, this type of operator can be used to find vegetation "equal to" Sierra-type mixed coniferous forest.

Relational operators.

Boolean operators such as "and", "or", and "not" allow you to chain logical tests. Like relational operators, Boolean operators return values of true and false. For example, you could find all slopes that are "greater-than" 45 degrees "and" that have an elevation that is "greater-than" 5000 meters.

Boolean operators.

The logical operators DIFF, IN, and OVER, also allow you to build logical tests on a cell-by-cell basis, but are implemented with specific rules.

• A DIFF B: If a cell value in raster A and raster B are different, the cell value in raster A is returned. If the cell values are the same, the value zero is returned.
• A IN {value list): If a cell value in raster A is in the value list, the cell value in raster A is returned. Otherwise, NoData is returned.
• A OVER B: If a cell value in raster A is not equal to zero, the cell value is raster A is returned. Otherwise, the cell value in raster B is returned.

Combinatorial operators combine the attributes of multiple input rasters. These operators find all unique combinations of values and assign a unique ID to each, which is then returned to the output grid. The output VAT will have the Value fields from all the input grids.

Combinatorial operators.

Bitwise operators are not used in this course, so they are not presented here. See the ArcGIS online help for details regarding the use of bitwise operators.