Map Algebra/Raster Calculator

ArcGIS Spatial Analyst includes advanced map algebra functions for combining multiple maps, performing suitability analysis, assigning weights, and identifying relationships.

Map algebra gives you the power to take real-world data and do advanced algebraic functions with this information.

Map algebra is the analysis language for Spatial Analyst. It is a simple syntax similar to any algebra. The input can be as simple as a single raster or feature data set. The manipulation can be multiplying each of the location's values by a conversion factor, or there can be a series of input raster or feature data sets to which the manipulation is applied such as when adding three raster data sets or layers together. Map algebra also allows you to build complex expressions and process them as a single command. For example, you can use a single expression to find all the cells within a specific elevation range, apply a unit conversion such as feet to meters, and calculate the slope at each of those cells. Such an expression might look like the following:

This graphic simply illustrates how mathematical operators and functions can be used to combine data on a cell-by-cell basis to derive new information.
Click on image to enlarge

Elev_meters = Elev_feet * 3.2808
Rain_total = Rain_April + Rain_May + Rain_June
Outgrid = (Con (elevation > 1000, Slope (elevation * 3.2808))

All ArcGIS Spatial Analyst functions can be used with map algebra syntax. Some of the more traditional mathematical operators and functions available are:

Abs
Divide
Exp
Exp10
Exp2
Float
Int
Ln
Log10
Log2
Minus
Mod
Negate
Plus
Power
Round Down
Round Up
Square
Square Root
Times
ACos
ACosH
ASin
ATan
ATan2
ATanH
Cos
CosH
Sin
SinH
Tan
TanH
Boolean And
Boolean Not
Boolean Or
Boolean Xor
Combinatorial And
Combinatorial Or
Combinatorial XOr
Equal To
Greater Than
Greater Than or Equal
Is Null
Less Than
Less Than or Equal
Not Equal
Test

Next: Local Statistics


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