Union (Coverage)


Computes the geometric intersection of two polygon coverages. All polygons from both coverages will be split at their intersections and preserved in the output coverage.

Learn more about how Union works


Union Illustration



Union_arc (in_cover, union_cover, out_cover, {fuzzy_tolerance}, {join_attributes})
ParameterExplanationData Type

The coverage whose polygons will be combined with the union coverage.


The union coverage whose polygons will be combined with the input coverage.


The output coverage that will be created containing the results of the operation.


The minimum distance between coordinates in the output coverage. By default, the minimum fuzzy tolerance value from the input and union coverages is used.

Learn more about how the default fuzzy tolerance is calculated


Specifies whether all items in both the input and the union coverage will be joined to the output coverage feature attribute table.

  • JOINAll items from both coverages will appear in the output coverage feature attribute table. If duplicate item names are encountered, the item in the input coverage will be maintained, and the one in the join file will be dropped. This is the default option and is used unless NO_JOIN is specified.
  • NO_JOINOnly the feature's internal number (cover#) from the input coverage and the union coverage are joined in the output coverage feature attribute table. This option is useful in reducing the size of the output coverage feature attribute table. The cover# field can then be used in the Add Join tool to link the features in the resulting coverage back to the features in the input or union coverage.

Code Sample

Union example (stand-alone script)

The following stand-alone script demonstrates how to union two coverages.

# Name: Union_Example.py
# Description: Unions two coverages
# Requirements: ArcInfo Workstation
# Author: ESRI

# Import system modules
import arcpy
from arcpy import env

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

# Set local variables
inCover = "tong_azone"
unionCover = "tong_flood2"
outCover = "C:/output/studyarea"
joinAttributes = "NO_JOIN"

# Execute Union
arcpy.Union_arc(inCover, unionCover, outCover, "", joinAttributes)


Related Topics

Licensing Information

ArcView: No
ArcEditor: No
ArcInfo: Requires ArcInfo Workstation installed

Published 6/8/2010