Working with operators in Map Algebra

In Map Algebra, operators apply a mathematical operation on input rasters and numbers.

Operators are generally placed between two inputs (operands) to perform a mathematical operation (for example, outVar = 3 + 7). In Map Algebra, operands can be rasters or numbers. To use an operator with a raster, the raster must be a Raster object.

The table below provides a quick reference indicating how current Map Algebra operators have been implemented in relation to Python operators and previous 9.x Map Algebra operators.

Operation	Python operator	Map Algebra operator	9.x Map Algebra operator *	Spatial Analyst GP tool
Arithmetic
Addition	+	+	+	Plus
Division	/	/	/, div	Divide
Integer Division	//	//	N/A	N/A
Modulo	%	%	Mod	Mod
Multiplication	*	*	*	Times
Power	**	**	N/A	Power
Subtraction	-	-	-	Minus
Unary Minus	-	-	-	Negate
Unary Plus	+	+	N/A	N/A
Boolean
Boolean And	N/A	&	&, and	Boolean And
Boolean Complement	N/A	~	^, not	Boolean Not
Boolean Exclusive Or	N/A	^	!, xor	Boolean XOr
Boolean Or	N/A	|	|, or	Boolean Or
Relational
Equal To	==	==	==, eq	Equal To
Greater Than	>	>	>, gt	Greater Than
Greater Than And Equal To	>=	>=	>=, ge	Greater Than Equal
Less Than	<	<	<, lt	Less Than
Less Than And Equal To	<=	<=	<=, le	Less Than Equal
Not Equal To	!=	!=	^=, <>, ne	Not Equal
Bitwise
Bitwise And	&	N/A	&&	Bitwise And
Bitwise Complement	~	N/A	^^	Bitwise Not
Bitwise Exclusive Or	^	N/A	!!	Bitwise XOr
Bitwise Left Shift	<<	<<	<<	Bitwise Left Shift
Bitwise Or	|	N/A	||	Bitwise Or
Bitwise Right Shift	>>	>>	>>	Bitwise Right Shift

* 9.x Map Algebra operator refers to the operator symbol you would have used in the Single Output Map Algebra tool or the Raster Calculator in the Spatial Analyst toolbar in ArcGIS versions 9.x and prior.

Operator rules

• When only numbers are used with operators, the result will be a number.

  # outVar will be assigned 10
  outVar = 3 + 7 

• When using operators with rasters, the raster must be a Raster object.

  outRas = Raster("inraster1") + Raster("inraster2")

• When a raster operand is used, then the result is a Raster object.

  # In the following statement, 4 is added to each cell value in inraster1
  outRas = Raster("inraster1") + 4  
  outRas2 = Raster("inraster") + math.pi

  In the above statement, pi is used from the Python math module. The math module also includes the base of the natural logarithm, math.e, which can also be used in a Map Algebra statement.

• Some operators can precede a Raster object or a number.

  outRas = -Raster("inraster")

• The Boolean (~, &, ^, |) operators will perform a Boolean operation when one or more input (operand) is a raster. If both inputs (operands) are numbers, then these operators will perform Bitwise operations.

Tip:

Spaces are not necessary between operators but are recommended for readability.

Tools and operators can be nested to create complex statements.

Learn more about building complex statements

Operator precedence

The precedence value determines the order in which operators are executed. The operator with the higher precedence will be processed first. If two operators have the same precedence value, then they will be processed in a left to right order in an expression.

You can use parentheses to override the precedence priority, with the operation in the deepest parentheses being processed first no matter what operator is specified.

The following table lists all the Map Algebra operators in order from lowest precedence to highest precedence. Each of the operators that are listed in the same row have the same precedence.

Map Algebra operator	Reference
<, <=, >, >=, ==, !=	Less Than, Less Than Equal, Greater Than, Greater Than Equal, Equal To, Not Equal
|	Boolean Or
^	Boolean XOr
&	Boolean And
<<, >>	Bitwise Left Shift, Bitwise Right Shift
+, -	Addition, Subtraction
*, /, //, %	Multiplication, Division, Integer Division, Modulo
+, -, ~	Unary Plus, Negate, Boolean Not
**	Power