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

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

• All input rasters must be integer. A floating-point raster must first be converted to an integer raster before it can be used in Weighted Overlay. The Reclassification tools provide an effective way to do the conversion.

• Each value class in an input raster is assigned a new value based on an evaluation scale. These new values are reclassifications of the original input raster values. A restricted value is used for areas you want to exclude from the analysis.

• Each input raster is weighted according to its importance or its percent influence. The weight is a relative percentage, and the sum of the percent influence weights must equal 100.

• Changing the evaluation scales or the percentage influences can change the results of the weighted overlay analysis.

Syntax

WeightedOverlay (in_weighted_overlay_table)

Parameter	Explanation	Data 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

Name	Explanation	Data 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

Current Workspace, Scratch Workspace, Output Coordinate System, Extent, Snap Raster, Cell Size, Mask

Licensing Information

ArcView: Requires Spatial Analyst

ArcEditor: Requires Spatial Analyst

ArcInfo: Requires Spatial Analyst