6 replies to this topic

[spesseh]

Hi,

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?

[Esther Mandeno]

Hi,

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:
http://support.esri....l...eway&GPID=5

Here's another method (looks complicated):
http://gis.utah.gov/...polygon-dataset

Not sure if either will work but you can give 'em a try.

Good luck!

[ceicher]

Hi,

It's not hard to do this using Geodatabase topology... now if only I can make it sound easy... ; )

(ArcCatalog)
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"

(ArcMap)
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

Good luck,

-Cory

[paul]

Geodatabase topology is a good way to go...as long as you have ArcEditor or ArcInfo licensing. If you have ArcView, you're out of luck.

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.

[Robert2009]

I would agree with Paul. That's the easy way to do it. You can try Feataure compare toolbox under Data Management Tools. This toolbox will allow you to run two features and will output results in a table.

Robert

[Ed Gage]

For the basic ArcView user, there are some useful topology tools in the ET Geowizards extension available at http://www.ian-ko.com/
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?

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[gregory]

Why not to try dissolve by area ?
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,
Gregory