IDW (Geostatistical Analyst)—ArcGIS Pro

Available with Geostatistical Analyst license.

Summary

Uses inverse distance weighted interpolation to predict a value for any unsampled location using the measured values surrounding the prediction location. The tool uses the assumption that things that are close to one another are more alike than those that are farther apart.

Learn more about how IDW works

Usage

The predicted value is limited to the range of the values used to interpolate. Because inverse distance weighted interpolation is a weighted distance average, the average cannot be greater than the highest or less than the lowest input data value. For example, it cannot predict ridges or valleys if the top of the ridge or bottom of the valley have not already been sampled.
Inverse distance weighted interpolation can produce contours at short distances around data locations (often called the bull's-eye effect).
Unlike other interpolation methods such as kriging, inverse distance weighted interpolation does not make explicit assumptions about the statistical properties of the input data. Inverse distance weighted interpolation is often used when the input data does not meet the statistical assumptions of more advanced interpolation methods.

Parameters

Label	Explanation	Data Type
Input features	The input point features containing the z-values to be interpolated.	Feature Layer
Z value field	Field that holds a height or magnitude value for each point. This can be a numeric field or the Shape field if the input features contain z-values or m-values.	Field
Output geostatistical layer (Optional)	The geostatistical layer produced. This layer is required output only if no output raster is requested.	Geostatistical Layer
Output raster (Optional)	The output raster. This raster is required output only if no output geostatistical layer is requested.	Raster Dataset
Output cell size (Optional)	The cell size at which the output raster will be created. This value can be explicitly set in the Environments by the Cell Size parameter. If not set, it is the shorter of the width or the height of the extent of the input point features, in the input spatial reference, divided by 250.	Analysis Cell Size
Power (Optional)	The exponent of distance that controls how quickly the weights decrease with distance. A higher power results in less influence from distant neighboring points. The value must be greater than or equal to 1. If no value is provided, a value will be estimated while the tool runs and displayed as a message. The estimated value will be the value that results in the lowest root-mean-square cross validation error.	Double
Search neighborhood (Optional)	Defines which surrounding points will be used to control the output. Standard is the default. Standard Major semiaxis—The major semiaxis value of the searching neighborhood. Minor semiaxis—The minor semiaxis value of the searching neighborhood. Angle—The angle of rotation for the axis (circle) or semimajor axis (ellipse) of the moving window. Max neighbors—The maximum number of neighbors that will be used to estimate the value at the unknown location. Min neighbors—The minimum number of neighbors that will be used to estimate the value at the unknown location. Sector Type—The geometry of the neighborhood. One sector—Single ellipse. Four sectors—Ellipse divided into four sectors. Four sectors shifted—Ellipse divided into four sectors and shifted 45 degrees. Eight sectors—Ellipse divided into eight sectors. Smooth Major semiaxis—The major semiaxis value of the searching neighborhood. Minor semiaxis—The minor semiaxis value of the searching neighborhood. Angle—The angle of rotation for the axis (circle) or semimajor axis (ellipse) of the moving window. Smoothing factor—The Smooth Interpolation option creates an outer ellipse and an inner ellipse at a distance equal to the Major Semiaxis multiplied by the Smoothing factor. The points that fall outside the smallest ellipse but inside the largest ellipse are weighted using a sigmoidal function with a value between zero and one. Standard Circular Radius—The length of the radius of the search circle. Angle—The angle of rotation for the axis (circle) or semimajor axis (ellipse) of the moving window. Max neighbors—The maximum number of neighbors that will be used to estimate the value at the unknown location. Min neighbors—The minimum number of neighbors that will be used to estimate the value at the unknown location. Sector Type—The geometry of the neighborhood. One sector—Single ellipse. Four sectors—Ellipse divided into four sectors. Four sectors shifted—Ellipse divided into four sectors and shifted 45 degrees. Eight sectors—Ellipse divided into eight sectors. Smooth Circular Radius—The length of the radius of the search circle. Smoothing factor—The Smooth Interpolation option creates an outer ellipse and an inner ellipse at a distance equal to the Major Semiaxis multiplied by the Smoothing factor. The points that fall outside the smallest ellipse but inside the largest ellipse are weighted using a sigmoidal function with a value between zero and one.	Geostatistical Search Neighborhood
Weight field (Optional)	Used to emphasize an observation. The larger the weight, the more impact it has on the prediction. For coincident observations, assign the largest weight to the most reliable measurement.	Field

arcpy.ga.IDW(in_features, z_field, {out_ga_layer}, {out_raster}, {cell_size}, {power}, {search_neighborhood}, {weight_field})

Name	Explanation	Data Type
in_features	The input point features containing the z-values to be interpolated.	Feature Layer
z_field	Field that holds a height or magnitude value for each point. This can be a numeric field or the Shape field if the input features contain z-values or m-values.	Field
out_ga_layer (Optional)	The geostatistical layer produced. This layer is required output only if no output raster is requested.	Geostatistical Layer
out_raster (Optional)	The output raster. This raster is required output only if no output geostatistical layer is requested.	Raster Dataset
cell_size (Optional)	The cell size at which the output raster will be created. This value can be explicitly set in the Environments by the Cell Size parameter. If not set, it is the shorter of the width or the height of the extent of the input point features, in the input spatial reference, divided by 250.	Analysis Cell Size
power (Optional)	The exponent of distance that controls how quickly the weights decrease with distance. A higher power results in less influence from distant neighboring points. The value must be greater than or equal to 1. If no value is provided, a value will be estimated while the tool runs and displayed as a message. The estimated value will be the value that results in the lowest root-mean-square cross validation error.	Double
search_neighborhood (Optional)	Defines which surrounding points will be used to control the output. Standard is the default. The following are Search Neighborhood classes: SearchNeighborhoodStandard, SearchNeighborhoodSmooth, SearchNeighborhoodStandardCircular, and SearchNeighborhoodSmoothCircular. Standard majorSemiaxis—The major semiaxis value of the searching neighborhood. minorSemiaxis—The minor semiaxis value of the searching neighborhood. angle—The angle of rotation for the axis (circle) or semimajor axis (ellipse) of the moving window. nbrMax—The maximum number of neighbors that will be used to estimate the value at the unknown location. nbrMin—The minimum number of neighbors that will be used to estimate the value at the unknown location. sectorType—The geometry of the neighborhood. ONE_SECTOR—Single ellipse. FOUR_SECTORS—Ellipse divided into four sectors. FOUR_SECTORS_SHIFTED—Ellipse divided into four sectors and shifted 45 degrees. EIGHT_SECTORS—Ellipse divided into eight sectors. Smooth majorSemiaxis—The major semiaxis value of the searching neighborhood. minorSemiaxis—The minor semiaxis value of the searching neighborhood. angle—The angle of rotation for the axis (circle) or semimajor axis (ellipse) of the moving window. smoothFactor—The Smooth Interpolation option creates an outer ellipse and an inner ellipse at a distance equal to the Major Semiaxis multiplied by the Smoothing factor. The points that fall outside the smallest ellipse but inside the largest ellipse are weighted using a sigmoidal function with a value between zero and one. Standard Circular radius—The length of the radius of the search circle. angle—The angle of rotation for the axis (circle) or semimajor axis (ellipse) of the moving window. nbrMax—The maximum number of neighbors that will be used to estimate the value at the unknown location. nbrMin—The minimum number of neighbors that will be used to estimate the value at the unknown location. sectorType—The geometry of the neighborhood. ONE_SECTOR—Single ellipse. FOUR_SECTORS—Ellipse divided into four sectors. FOUR_SECTORS_SHIFTED—Ellipse divided into four sectors and shifted 45 degrees. EIGHT_SECTORS—Ellipse divided into eight sectors. Smooth Circular radius—The length of the radius of the search circle. smoothFactor—The Smooth Interpolation option creates an outer ellipse and an inner ellipse at a distance equal to the Major Semiaxis multiplied by the Smoothing factor. The points that fall outside the smallest ellipse but inside the largest ellipse are weighted using a sigmoidal function with a value between zero and one.	Geostatistical Search Neighborhood
weight_field (Optional)	Used to emphasize an observation. The larger the weight, the more impact it has on the prediction. For coincident observations, assign the largest weight to the most reliable measurement.	Field

Code sample

IDW example 1 (Python window)

Interpolate a series of point features onto a raster.

import arcpy
arcpy.env.workspace = "C:/gapyexamples/data"
arcpy.ga.IDW("ca_ozone_pts", "OZONE", "outIDW", "C:/gapyexamples/output/idwout", "2000", "2",
             arcpy.SearchNeighborhoodStandard(300000, 300000, 0, 15, 10, "ONE_SECTOR"), "")

IDW example 2 (stand-alone script)

Interpolate a series of point features onto a raster.

# Name: InverseDistanceWeighting_Example_02.py
# Description: Interpolate a series of point features onto a rectangular raster
#              using Inverse Distance Weighting (IDW).
# Requirements: Geostatistical Analyst Extension

# Import system modules
import arcpy

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

# Set local variables
inPointFeatures = "ca_ozone_pts.shp"
zField = "OZONE"
outLayer = "outIDW"
outRaster = "C:/gapyexamples/output/idwout"
cellSize = 2000.0
power = 2

# Set variables for search neighborhood
majSemiaxis = 300000
minSemiaxis = 300000
angle = 0
maxNeighbors = 15
minNeighbors = 10
sectorType = "ONE_SECTOR"
searchNeighbourhood = arcpy.SearchNeighborhoodStandard(majSemiaxis, minSemiaxis,
                                                       angle, maxNeighbors,
                                                       minNeighbors, sectorType)

# Execute IDW
arcpy.ga.IDW(inPointFeatures, zField, outLayer, outRaster, cellSize, 
             power, searchNeighbourhood)

Environments

Cell Size, Coincident Points, Current Workspace, Extent, Geographic Transformations, Mask, Output Coordinate System, Parallel Processing Factor, Snap Raster

Licensing information

Basic: Requires Geostatistical Analyst
Standard: Requires Geostatistical Analyst
Advanced: Requires Geostatistical Analyst