IDW (3D Analyst)


Interpolates a raster surface from points using an inverse distance weighted (IDW) technique.

Learn more about how IDW works



Idw_3d (in_point_features, z_field, out_raster, {cell_size}, {power}, {search_radius}, {in_barrier_polyline_features})
ParameterExplanationData Type

The input point features containing the z-values to be interpolated into a surface raster.

Feature Layer

The field that holds a height or magnitude value for each point.

This can be a numeric field or the Shape field if the input point features contain z-values.


The output interpolated surface raster.

Raster Layer

The cell size at which the output raster will be created.

This will be the value in the environment if it is explicitly set; otherwise, 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

The exponent of distance.

Controls the significance of surrounding points on the interpolated value. A higher power results in less influence from distant points. It can be any real number greater than 0, but the most reasonable results will be obtained using values from 0.5 to 3. The default is 2.


Defines which of the input points will be used to interpolate the value for each cell in the output raster.

There are two ways to specify the specify the searching neighborhood: Variable and Fixed.

Variable uses a variable search radius in order to find a specified number of input sample points for the interpolation. Fixed uses a specified fixed distance within which all input points will be used. Variable is the default.

The syntax for these parameters are:

  • Variable, number_of_points, maximum_distance, where:
    • number_of_points—An integer value specifying the number of nearest input sample points to be used to perform interpolation. The default is 12 points.
    • maximum_distance—Specifies the distance, in map units, by which to limit the search for the nearest input sample points. The default value is the length of the extent's diagonal.
  • Fixed, distance, minimum_number_of_points, where:
    • distance—Specifies the distance as a radius within which input sample points will be used to perform the interpolation. The value of the radius is expressed in map units. The default radius is five times the cell size of the output raster.
    • minimum_number_of_points—An integer defining the minimum number of points to be used for interpolation. The default value is 0.

      If the required number of points is not found within the specified distance, the search distance will be increased until the specified minimum number of points is found.

      When the search radius needs to be increased it is done so until the minimum_number_of_points fall within that radius, or the extent of the radius crosses the lower (southern) and/or upper (northern) extent of the output raster. NoData is assigned to all locations that do not satisfy the above condition.


Polyline features to be used as a break or limit in searching for the input sample points.

Feature Layer

Code Sample

IDW example 1 (Python window)

This example inputs a point shapefile and interpolates the output surface as a TIFF raster.

import arcpy
from arcpy import env  
env.workspace = "C:/data"
arcpy.Idw_3d("ozone_pts.shp", "ozone", "C:/output/idwout.tif", 2000, 2, 10)
IDW example 2 (stand-alone script)

This example inputs a point shapefile and interpolates the output surface as a Grid raster.

# Name:
# Description: Interpolate a series of point features onto a
#    rectangular raster using Inverse Distance Weighting (IDW).
# Requirements: 3D Analyst Extension

# Import system modules
import arcpy
from arcpy import env

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

# Set local variables
inPointFeatures = "ca_ozone_pts.shp"
zField = "ozone"
outRaster = "C:/output/idwout01"
cellSize = 2000.0
power = 2
searchRadius = 150000

# Check out the ArcGIS 3D Analyst extension license

# Execute IDW
arcpy.Idw_3d(inPointFeatures, zField, outRaster, cellSize, 
             power, searchRadius)


Related Topics

Licensing Information

ArcView: Requires 3D Analyst or Spatial Analyst
ArcEditor: Requires 3D Analyst or Spatial Analyst
ArcInfo: Requires 3D Analyst or Spatial Analyst