topic Re: Union polygons in Geoprocessing Questions

Union polygons

MilaReady__GISP — Mon, 16 May 2011 14:32:22 GMT

Good morning,

I have about 400 shapefiles, each containing one polygon, that I would like to combine into one master. I need to remove numerous fields since each GPS unit used to collect the data has different default fields/properties. Additionally, I need to add several fields for queries which are not defaults for any GPS units (i.e. Permit #, Date, Mineral, Status, etc). So, how to proceed? I am new to ArcInfo, and there is currently no geodatabase structure in place. Thank you very much!

Re: Union polygons

DarrenWiens2 — Mon, 16 May 2011 15:03:47 GMT

If you want to planarize overlapping features (squish them into one feature), use the Union tool. If you don't want to planarize overlapping features (keep overlapping features separate), use the Merge tool. I don't know if there is a limit to the number of shapefiles you can combine at once. Then, use Delete Field to drop fields. Use Add Field to add each field.

Re: Union polygons

MilaReady__GISP — Mon, 16 May 2011 20:13:17 GMT

Darren,
Thanks for the help. I have the tables behind each shapefile cleaned up and ready to perform the union. However, I keep getting "Error 000210: Cannot create output". I have tried the Repair Geometry tool, but it also produces "Error 111461: Repaired feature 0 because of self intersections". Any futher suggestions? Thanks in advance!

Re: Union polygons

DarrenWiens2 — Tue, 17 May 2011 14:17:32 GMT

Can you post a few of your polygon files?

Re: Union polygons

MilaReady__GISP — Wed, 18 May 2011 15:50:49 GMT

The zip file contains two of my problematic files... the attribute tables and field properties are identical, and I am hoping to avoid having to edit every bad polygon by hand. Any thoughts would be greatly appreciated!
~Mila

Re: Union polygons

DarrenWiens2 — Wed, 18 May 2011 16:08:23 GMT

Your polygons have many tiny, tiny segments which I think are confusing ArcMap. I assume the equipment used to create these polygons are not accurate to within millimetres. You should import them into a geodatabase and adjust the xy tolerance to reflect the accuracy of your data. This should simplify your polygons into something useable (I used the Feature to Polygon tool with an xy tolerance of 0.1m and then Union, and it worked fine).

Re: Union polygons

marcie_elenemarcus — Wed, 03 Aug 2011 02:11:42 GMT

hye,

I have 200 shapefiles (polygons) which I need to union them all into one layer. I need union it in order the overlapping could shows the intensity area. however, i am having problem to union all of the shapefiles. Why this is happening? i only manage to union like 65 files of the shapefiles... the ERROR 000210: Cannot create output... Failed to execute (Union).
keeps on popping out... it is stressing me out. i could not do the next step (which is to know the intensity of the overlapping area) if i could not manage to union all of these shapefiles..

Can somebody help me? http://forums.arcgis.com/images/icons/icon9.png

Re: Union polygons

EvaWillerslev — Sun, 21 Aug 2011 09:22:29 GMT

Mila Ready,

I had a look at your polygons in the attached zip file, and one of them turned out to contain intersections, which some geoprocessing tools like UNION can't handle. You'll need to repair the geometry of your polygons using the Repair Geometry Tool (ArcToolbox - Data Management Tools - Features Repair Geometry).

Secondly, prior to using the UNION tool, you need to specify the geographical extent of the new UNION-shapefiles you are creating. Right click ArcToolbox, open Environments, go to Processing Extents, set the Extent to "Union of Inputs", click OK. Then right click ArcToolbox again, and save the settings to default.

I tried it and it worked for me.

Note: If you have an ArcInfo license you can union as many polygon shapefiles as you like, but if you are using ArcView you can union only two at a time.

Hope this helps,

Eva Willerslev