Thiessen (Coverage)
Summary
Converts input coverage points to an output coverage of Thiessen proximal polygons.
Illustration
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Usage
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Thiessen polygons have the unique property that each polygon contains only one input point, and any location within a polygon is closer to its associated point than to the point of any other polygon.
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To ignore close points, specify a proximal tolerance. For point coverages with an automation scale between 1:10,000 and 1:100,000, try a tolerance between 1.668 ft (0.508 m) and 16.620 ft (5.080 m).
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The Output Coverage inherits these data model contents from the Input Coverage: items from the point attribute table, tics, and the projection file.
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Thiessen polygons can be used to apportion a point coverage into regions known as Thiessen or Voronoi polygons. Each region contains only one Input Coverage point. Each region has the unique property that any location within a region is closer to the region's point than to the point of any other region.
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All items in the Input Coverage point attribute table (PAT) are copied to their associated polygons in the Output Coverage PAT.
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The Output Coverage polygon label points are located at the same positions as the Input Coverage points.
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If the Input Coverage has a PRJ file, it is copied to the Output Coverage.
Syntax
| Parameter | Explanation | Data Type |
in_cover |
The coverage that must have a point feature attribute table created by BUILD with the POINT option. | Coverage |
out_cover |
The polygon coverage in which the Thiessen proximal polygons will be produced. | Coverage |
proximal_tolerance (Optional) |
Tolerance used to eliminate Input Coverage points that fall within the specified distance of other Input Coverage points. The default Proximal Tolerance is the machine precision of the computer. | Double |
Code Sample
The following stand-alone script demonstrates how to create a thiessen proximal polygon around each well in a point coverage.
# Name: Thiessen_Example.py
# Description: Creates a thiessen area around each well in a point coverage.
# Requirements: ArcInfo Workstation
# Import system modules
import arcpy
from arcpy import env
# Set environment settings
env.workspace = "C:/data"
# Set local variables
inCover = "wells"
outCover = "C:/output/wellareas"
# Execute Thiessen
arcpy.Thiessen_arc (inCover, outCover, "")