ArcMap

Weighted Sum

Available with Spatial Analyst license.

Summary

Overlays several rasters, multiplying each by their given weight and summing them together.

Learn more about how Weighted Sum works

Illustration

Weighted Sum illustration
In the illustration, the cell values are multiplied by their weight factor, and the results are added together to create the output raster. For example, consider the upper left cell. The values for the two inputs become (2.2 * 0.75) = 1.65 and (3 * 0.25) = 0.75. The sum of 1.5 and 0.75 is 2.4.

Usage

  • A useful way to add several rasters together is to input multiple rasters and set all weights equal to 1.

  • Input rasters can be integer or floating point.

  • The weight values can be any positive or negative decimal value. It is not restricted to a relative percentage nor does it need to be equal to 1.0.

  • The weight will be applied to the specified field for the input raster. Fields can be of type short or long integer, double or float.

  • By default, this tool will take advantage of multi-core processors. The maximum number of cores that can be used is four.

    If you want the tool to use fewer cores, use the parallelProcessingFactor environment setting.

  • See Analysis environments and Spatial Analyst for additional details on the geoprocessing environments that apply to this tool.

Syntax

WeightedSum(in_rasters)
ParameterExplanationData Type
in_rasters

TheWeighted Sum tool overlays several rasters, multiplying each by their given weight and summing them together.

An Overlay class is used to define the table. The WSTable object is used to specify a Python list of input rasters and weight them accordingly.

The form of the object is:

  • WSTable(weightedSumTable)

WSTable

Return Value

NameExplanationData Type
out_raster

The output weighted raster.

It will be of floating-point type.

Raster

Code sample

WeightedSum example 1 (Python window)

This example creates a suitability raster for locating a ski resort by combining multiple rasters together and applying appropriate weight factors.

import arcpy
from arcpy import env  
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"

# Execute WeightedSum
outWeightedSum = WeightedSum(WSTable([["snow", "VALUE", 0.25], ["land", "VALUE",0.25],
									  ["soil", "VALUE", 0.5]]))
outWeightedSum.save("C:/sapyexamples/output/outwsum")
WeightedSum example 2 (stand-alone script)

This example creates a suitability raster for locating a ski resort by combining multiple rasters together and applying appropriate weight factors.

# Name: WeightedSum_Ex_02.py
# Description: Overlays several rasters multiplying each by their given
#    weight and summing them together.
# Requirements: Spatial Analyst Extension

# Import system modules
import arcpy
from arcpy import env
from arcpy.sa import *

# Set environment settings
env.workspace = "C:/sapyexamples/data"

# Set local variables
inRaster1 = "snow"
inRaster2 = "land"
inRaster3 = "soil"
WSumTableObj = WSTable([[inRaster1, "VALUE", 0.25], [inRaster2, "VALUE", 0.25],
                        [inRaster3, "VALUE", 0.5]])

# Check out the ArcGIS Spatial Analyst extension license
arcpy.CheckOutExtension("Spatial")

# Execute WeightedSum
outWeightedSum = WeightedSum(WSumTableObj)

# Save the output 
outWeightedSum.save("C:/sapyexamples/output/weightsumout")

Environments

Licensing information

  • Basic: Requires Spatial Analyst
  • Standard: Requires Spatial Analyst
  • Advanced: Requires Spatial Analyst

Related topics