Union (Coverage) (ArcInfo only)

Usage tips

• The input coverage and the union coverage must have polygon topology.

• Region subclasses in either the input or union coverage are maintained in the output coverage. Subclasses with identical names and attribute schemas are appended.

• Label points are generated in each output coverage polygon. The new polygon User-IDs are set equal to the polygon internal number minus one.

• The input coverage, union coverage, and output coverage must have different names, even when in different workspaces.

• Existing input coverage annotation is copied to the output coverage by UNION.

• Route systems in the input coverage will be maintained in the output coverage. However, UNION on routes and sections themselves is not permitted.

• Region subclasses from both input coverage and union coverage are maintained. If the same subclass exists in both coverages, the subclass contents are appended. If the same subclass exists in both coverages but the item definitions are different, a message is given and the subclass is not propagated.

• The coordinate precision of the output coverage is determined by the Precision for Derived Coverages environment.

• Projection files will be compared for similarity using the level of comparison specified in the Compare Projections environment.

• On single-precision coverages, UNION calculates a minimum tolerance based on the mathematical precision of the coverage (based on the width of the BND and the number of decimal places). If the calculated minimum tolerance is greater than the fuzzy tolerance entered, the calculated minimum tolerance is used.

• Learn more about data model content inherited by the output.

• Learn more about how the default fuzzy tolerance is calculated.

• Learn more about processing planar graphs.

• The following environments affect this tool: derivedPrecision, newPrecision, projectCompare, scratchWorkspace, and current workspace.

Command line syntax
An overview of the Command Line window
Union_arc <in_cover> <union_cover> <out_cover> {fuzzy_tolerance} {JOIN | NO_JOIN}

Command line example

union_arc h:\workspace\soil h:\workspace\timber h:\final\tiber_soil_un 0.0003 NO_JOIN

Scripting syntax
About getting started with writing geoprocessing scripts
Union_arc (in_cover, union_cover, out_cover, fuzzy_tolerance, join_attributes)

Script example

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

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

# Put in error trapping in case an error occurs when running tool
try:
    # 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")

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