Union (Coverage)

This tool only works with an ArcInfo license and will only be available in ArcToolbox if you have installed ArcInfo Workstation.

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

Usage tips


Union_arc (in_cover, union_cover, out_cover, fuzzy_tolerance, join_attributes)
Parameter Explanation Datatype
Input Coverage (Required)

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

Union Coverage (Required)

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

Output Coverage (Required)

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

Fuzzy Tolerance (Optional)

The minimum distance between coordinates in the output coverage. By default, the minimum fuzzy tolerance value from the input and erase coverages is used. Learn more about how the Default Fuzzy Tolerance is Calculated

Join Attributes (Optional)

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

  • JOIN—All 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_JOIN—Only 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.

Data types for geoprocessing tool parameters

Script Example

# SimpleUnion.py
# Description: Simple example of using Union in a python script
# Requirements: Python and the Python win32all extension
# Author: ESRI
# Data 1/1/2004

# Create the Geoprocessor
import arcgisscripting
gp = arcgisscripting.create()

# Put in error trapping in case an error occurs when running tool
    # Union the parcels and counties to get the polys from both of these into one coverage
    gp.workspace = "c:/work/gisdata"
    gp.Union_arc("parcels", "counties","parcels2")

    # If an error occurred print the message to the screen
    print gp.GetMessages()

See Also

  • Identity (Analysis)
  • Identity (Coverage)
  • Intersect (Coverage)