Weighted Overlay (Spatial Analyst)

Summary

Overlays several rasters using a common measurement scale and weights each according to its importance.

Learn more about how Weighted Overlay works

Illustration

Weighted Overlay illustration
In the illustration, the two input rasters have been reclassified to a common measurement scale of 1 to 3. Each raster is assigned a percentage influence. The cell values are multiplied by their percentage influence, and the results are added together to create the output raster. For example, consider the top left cell. The values for the two inputs become (2 * 0.75) = 1.5 and (3 * 0.25) = 0.75. The sum of 1.5 and 0.75 is 2.25. Because the output raster from Weighted Overlay is integer, the final value is rounded to 2.

Usage

Syntax

WeightedOverlay (in_weighted_overlay_table)
ParameterExplanationData Type
in_weighted_overlay_table

The Weighted Overlay tool allows the calculation of a multiple-criteria analysis between several rasters.

An Overlay class is used to define the table. The WOTable object is used to specify the criteria rasters and their respective properties.

The form of the object is:

  • WOTable([[inRaster, influence, field, remap],...], [from, to, by])

WOTable

Return Value

NameExplanationData Type
out_raster

The output suitability raster.

Raster

Code Sample

WeightedOverlay example 1 (Python window)

This example create a suitability IMG raster that identifies potential site locations for a ski area.

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

outsuit = WeightedOverlay(WOTable(
           [
            ["snow", 50, 'VALUE', RemapValue([[1,"Nodata"],[5,3],[9,10],["NODATA","NODATA"]])], 
            ["land", 20, '', RemapValue([["water","1"],["forest",5],["open field",9],["NODATA", "NODATA"]])],
            ["soil", 30, 'VALUE', RemapValue([[1,"Restricted"],[5,5],[7,7],[9,9],["NODATA", "Restricted"]])]
           ],[1,9,1]))
outsuit.save("C:/sapyexamples/output/outsuit.img")
WeightedOverlay example 2 (stand-alone script)

This example create a suitability IMG raster that identifies potential site locations for a ski area.

# Name: WeightedOverlay_Ex_02.py
# Description: Overlays several rasters using a common scale and weighing 
#    each according to its importance.
# Requirements: Spatial Analyst Extension
# Author: ESRI

# 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"

remapsnow = RemapValue([[0,1],[1,1],[5,5],[9,9],["NODATA","NODATA"]])
remapland = RemapValue([[1,1],[5,5],[6,6],[7,7],[8,8],[9,9],["NODATA","Restricted"]])
remapsoil = RemapValue([[0,1],[1,1],[5,5],[6,6],[7,7],[8,8],[9,9],["NODATA", "NODATA"]])

myWOTable = WOTable([[inRaster1, 50, "VALUE", remapsnow],
                     [inRaster2, 20, "VALUE", remapland], 
                     [inRaster3, 30, "VALUE", remapsoil]
					          ], [1, 9, 1])    

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

# Execute WeightedOverlay
outWeightedOverlay = WeightedOverlay(myWOTable)

# Save the output
outWeightedOverlay.save("C:/sapyexamples/output/weightover2")

Environments

Related Topics

Licensing Information

ArcView: Requires Spatial Analyst
ArcEditor: Requires Spatial Analyst
ArcInfo: Requires Spatial Analyst

6/29/2011