Check for duplicate polygons
Posted 31 August 2009 - 08:53 AM
I have a shapefile of administative units. I want to confirm that there are no polygons that are lying on top of each other.
How can i do this easily within arcgis?
That's a good question. I don't have an answer for it. My databases are usually not very big and I just check each one individually, but then again, haven't really come across this problem.
I did a quick search on the ESRI online support and found this:
Here's another method (looks complicated):
Not sure if either will work but you can give 'em a try.
Life is like riding a bicycle. To keep your balance you must keep moving. - Albert Einstein
Posted 01 September 2009 - 10:57 AM
It's not hard to do this using Geodatabase topology... now if only I can make it sound easy... ; )
1. get your polygon data in a geodatabase feature class (e.g. in a file geodatabase) (in a feature dataset)
2. create a new topology in the same feature dataset
3. add one rule "Must Not Overlap"
4. create the topology. when prompted, say "Yes, validate topology"
5. start arcmap
6. drag drop your topology into ArcMap
7. start editing
8. Open Error Inspector and you'll see all overlapping polys as errors.
After making edits, simply re-run the validation to find any new errors.
ESRI help is online here: http://support.esri....webHelp.gateway
Recommended ArcGIS Desktop Help topics:
Creating a topology
Validating a topology
Posted 01 September 2009 - 12:28 PM
If you have ArcView licensing, you could try calculating the centroid of polygon using Calculate Geometry, and sort the result ascending. If the centroid has the same coordinate as another polygon, it's a safe bet it's a duplicate.
Manifold has some slick tools for finding duplicates, if you happen to have a copy of that software.
Posted 01 September 2009 - 02:19 PM
Posted 02 September 2009 - 03:46 PM
The unregistered version is free, and contains several polygon functions that have come in handy for the kinds of issues you mention (e.g. eliminating duplicates, slivers, etc.), although there might be size limitations for the free version. Assuming that the duplicate features have the same attribute information, could you also simply use the dissolve geoprocessing tool that comes with ArcView?
Posted 02 September 2009 - 04:14 PM
Duplicated polygons should have the same areas
You can compare the number of shapes before and after that operation get an answer if there were any, and get what you want.
Hope it helps,
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