I have a shapefile with polygons representing unique populations. I want to determine contiguous polygons in my shapefile, and then extract the border separating contiguous polygons as a separate polyline file. Importantly, I require the created polyline file to indicate the two polygons it separates.

I am aware of Polygon Neighbor to produce a table of all contiguous pairs, but this doesn't help me extract borders as polylines.

Consider group A in the following example map:

Example Border

Group A has 8 contiguous pairs: AB, AC, AD, AE, AF, AG, AH, AI. I would like the output file to separate the aggregate border for group A into 8 separate lines, each line referencing only the shared border between each contiguous pair; e.g., the border of AH in red would be a single line in the output data. As noted before it is important that the output file also identifies the two groups each line separates.

To clarify, I require a general solution for all possible contiguous pairs in my dataset. I do not have a single group such as the example group A that I am interested in.

This question is similar to Extracting polyline of border between differing polygons using R or GRASS?, except I'm interested in a solution using ArcGIS 10.2 for Desktop. I have some knowledge of Python if an ArcPy solution is easiest.

  • 1
    If you need to identify from the polylines which polygons are on either side use Polygon to Line help.arcgis.com/EN/arcgisdesktop/10.0/help/index.html#//… and specify IDENTIFY_NEIGHBORS (advanced license required) It would be best if you didn't use shapefiles as the FIDs are not static, preferably convert the polygon shapefile to a geodatabase feature class (with static OIDs) so that the ids are reliable. Sep 8, 2015 at 22:12
  • @MichaelMiles-Stimson: If I am able to figure out how to extract borders as polylines I will follow your suggestion. Thanks!
    – acd
    Sep 8, 2015 at 22:39
  • That's what the tool does. Where polygons coalesce only one line is produced and if you specify it will store the OID/FID of the source polygons in a field. Sep 8, 2015 at 22:48
  • @MichaelMiles-Stimson: Sorry I didn't read your comment correctly the first time around. Thank you for the response, I was able to almost do what I want with your suggestion. I say almost because approximately 1/5 of the polylines produced are disjoint; e.g., a single border segment might be split into 3 disjoint polylines, where one line has the appropriate left/right FIDs, but then the other two have only one of the FIDs and an unmatched FID of -1 for the other. Is this a common problem you are aware of?
    – acd
    Sep 9, 2015 at 20:13
  • Yes it's a common problem, because of tiny gaps in the polygons the lines diverge and are populated with -1 (no polygon) on the outside. A tool like Eliminate or Integrate (see gis.stackexchange.com/questions/11004/… or gis.stackexchange.com/questions/154264/… - read the warnings) will help close the gaps, after the gaps are removed you should have single lines at the boundaries. Sep 9, 2015 at 21:39

1 Answer 1


This will convert your polygons into arcs very quickly. You need 2 layers in table of content: 1st - polylines, 2nd - polygons

import arcpy, traceback, os, sys,time
from arcpy import env
env.overwriteOutput = True

    def showPyMessage():
        arcpy.AddMessage(str(time.ctime()) + " - " + message)

    mxd = arcpy.mapping.MapDocument("CURRENT")
    curT = arcpy.da.InsertCursor(theLinksLayer,"SHAPE@")
    with arcpy.da.SearchCursor(PGONS, "Shape@") as cursor:
        for row in cursor:
            feat = row[0].boundary()
    arcpy.Dissolve_management(theLinksLayer, dissolved,"","", "SINGLE_PART")
    arcpy.AddMessage("Dissolving ...")
    curT = arcpy.da.InsertCursor(theLinksLayer,"SHAPE@")
    with arcpy.da.SearchCursor(dissolved, "SHAPE@") as cursor:
        for row in cursor:

    arcpy.AddMessage("\nPolygons unbuilt into %i lines\n" %m)
    del curT

    message = "\n*** PYTHON ERRORS *** "; showPyMessage()
    message = "Python Traceback Info: " + traceback.format_tb(sys.exc_info()[2])[0]; showPyMessage()
    message = "Python Error Info: " +  str(sys.exc_type)+ ": " + str(sys.exc_value) + "\n"; showPyMessage()

From here it is enough to spatially join lines to polygons (one to many, SHARE_A_LINE_SEGMENT_WITH) and dissolve output using line name and first, last polygon IDs to get this:

enter image description here

  • Thank you for the very thorough response. I apologize but I am not following something very basic in your explanation. I am confused where the 1st polyline layer in the Table of Contents is coming from? My aim is to create a polyline layer of contiguous border segments so I don’t understand how to add it to the Table of Contents in the first place. Thank you.
    – acd
    Sep 9, 2015 at 0:40
  • Create empty polyline feature layer. Make it sitting on the top of all the other layers. Place your source polygons layer below it.
    – FelixIP
    Sep 9, 2015 at 1:06
  • To be honest there many other ways to derive polygon edges as Michael said. You might start editing empty polyline layer. Select all polygons, copy-paste to polyline layer. Go advanced editing, pick planarise. I offered script simply because it is sitting in one of my custom toolboxes and I preffer to use it
    – FelixIP
    Sep 9, 2015 at 1:18
  • Thank you. I am learning to use script so I am slow but I prefer to do it this way. I created an empty polyline feature layer, placed it at the top, followed by my source polygon layer. When running the script I keep getting the error message: ERROR 999999: Error executing function. Cannot acquire a lock. Cannot acquire a lock. Failed to execute (Dissolve). I am unable to determine why the layers are locked when using the Dissolve tool?
    – acd
    Sep 9, 2015 at 1:56
  • Try to change dissolved="in_memory/dissolved" to something like dissolved=r"c:\work\dissolved.shp". in_memory storage can be tricky. Also disable arcpy.Delete_management(in_memory). Note that I've added escept block at the end of script. No idea why it wasn't best at the start. Python is good, don't give up
    – FelixIP
    Sep 9, 2015 at 2:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.