ArcMap

Extract by Polygon

Available with Spatial Analyst license.

Summary

Extracts the cells of a raster based on a polygon.

Illustration

Extract by Points illustration
OutRas = ExtractByPolygon(InRas1,[Point(1.4,0.4),Point(1.4,4.6),Point(3.6,4.6),Point(5.6,2.6),Point(3.6,0.4),Point(1.4,0.4)],"INSIDE")

Usage

  • To extract based on a polygon in a feature class instead of providing a series of x,y pairs, you can use the Extract By Mask tool.

  • The center of the cell is used to determine whether a cell is inside or outside a polygon. If the center is within the arcs of the polygon, the cell is considered fully inside even if portions of the cell fall outside the polygon.

  • The polygon has a limit of 1,000 vertices. Polygon vertices must be entered in a clockwise order. The first and last vertex must be the same to close each polygon if multiple polygons are to be used. If the last points are not identical, the polygon will be closed automatically. The arcs of the polygon can cross one another, but convoluted polygons are not recommended.

  • Cell locations that are not selected are assigned a value of NoData.

  • When a multiband raster is specified as input, a new multiband raster will be created as output. Each individual band in the input multiband raster will be analyzed accordingly.

    The default output format is a geodatabase raster. If an Esri Grid stack is specified as the output format, note that the name cannot start with a number, use spaces, or be more than nine characters in length.

  • If the input is a layer created from a multiband raster with more than three bands, the extraction operation will only consider the bands that were loaded (symbolized) by the layer. As a result, the output multiband raster can only have three bands, corresponding to those used in the display of the input layer.

  • If the input raster is integer, the output raster will be integer. If the input is floating point, the output will be floating point.

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

Syntax

ExtractByPolygon (in_raster, polygon, {extraction_area})
ParameterExplanationData Type
in_raster

The input raster from which cells will be extracted.

Raster Layer
polygon
[point,...]

A polygon (or polygons) that defines the area of the input raster to be extracted.

Each polygon part is a list of vertices defined by Point classes. Optionally a Polygon class can be used to define a list of polygon parts.

The points are specified as x,y coordinate pairs in the same map units as the input raster. The form of the object is:

  • [[point(x1,y1), point(x2,y2), point(xn,yn), ..., point(x1,y1)], [point(x'1,y'1), point(x'2,y'2), point(x'n,y'n), ..., point(x'1,y'1)], ...]

Note that the last coordinate should be the same as the first in order to close a polygon.

Point
extraction_area
(Optional)

Identifies whether to extract cells inside or outside the input polygon.

  • INSIDE — A keyword specifying that the cells inside the input polygon should be selected and written to the output raster. All cells outside the polygon will receive NoData values on the output raster.
  • OUTSIDE — A keyword specifying that the cells outside the input polygon should be selected and written to the output raster. All cells inside the polygon will receive NoData values on the output raster.
String

Return Value

NameExplanationData Type
out_raster

The output raster containing the cell values extracted from the input raster.

Raster

Code sample

ExtractByPolygon example 1 (Python window)

This example extracts cells from a raster based on the defined polygon coordinates.

import arcpy
from arcpy import env
from arcpy.sa import *
polyPoints = [arcpy.Point(743050, 4321275), arcpy.Point(743100, 4321200), 
             arcpy.Point(743500, 4322000),arcpy.Point(742900, 4321800)]
env.workspace = "C:/sapyexamples/data"
extPolygonOut = ExtractByPolygon("soil", polyPoints, "INSIDE")
extPolygonOut.save("c:/sapyexamples/output/extpoly")
ExtractByPolygon example 2 (stand-alone script)

This example extracts cells from a raster based on the defined polygon coordinates.

# Name: ExtractByPolgyon_Ex_02.py
# Description: Extracts the cells of a raster based on a polygon.
# 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
inRaster = "soil"
polyPoints = [arcpy.Point(743050, 4321275), arcpy.Point(743100, 4321200), 
             arcpy.Point(743500, 4322000),arcpy.Point(742900, 4321800)]

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

# Execute ExtractByPolygon
extPolygonOut = ExtractByPolygon(inRaster, polyPoints, "INSIDE")

# Save the output 
extPolygonOut.save("c:/sapyexamples/output/extpoly02")

Environments

Licensing information

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

Related topics