topic Re: Merging polygons that are close together in Geoprocessing Questions

Merging polygons that are close together

MTGIS — Wed, 14 May 2014 06:37:23 GMT

Hello,

I have a polygon shapefile of grassland habitat. At present there are just over 1000 polygons. However this is an over-representation. What I wish to do is to merge the polygons that are close together (within 1 metre of each other) so the register as just one polygon in the attribute table. Can anyone advise how I can achieve this?

Thanks
Michael

Re: Merging polygons that are close together

JimCousins — Wed, 14 May 2014 12:46:25 GMT

Michael,
You could run the buffer tool with a 1 meter distance, and dissolve all option. then buffer again at -1 meter to shrink the overall extent. Of course, if the 1 meter increase does not matter for your analysis, leave them as the first result. There will be some small distortion due to the buffer out and in, but probably not too much, unless your polygons are quite convoluted.
Best Regards,
Jim

Re: Merging polygons that are close together

MTGIS — Wed, 14 May 2014 13:38:42 GMT

Thanks Jim. That was actually one idea I had. It does indeed work, but as you mention it does generate a bit of distortion, so I thought there may be a better way. I think what I may need is the aggregate tool, but I don't have the license for that unfortunately.
Thanks, Michael

Re: Merging polygons that are close together

RichardFairhurst — Wed, 14 May 2014 14:11:03 GMT

1. Perform the Buffer with a .5 meter width (so that 2 separate shapes will just touch at 1 meter) and the Dissolve List option using whatever fields you want to retain in your analysis.
2. Use the Multipart to Singlepart tool on the buffers.
3. Add a long field to the Buffers and Calculate the ObjectID values of the buffers into it.
4. Spatial Join the original shapes to the Buffer.
5. Dissolve the spatially joined shapes on the fields you want to retain in your analysis plus the field you added to the buffer holding the buffer ObjectID values using the multipart option.

The resulting shapes will be exactly the same as the original shapes, except that they will be merged together to form a multipart feature only where they share the fields you want to analyze and are within 1 meter of each other. The Dissolve on fields you want to retain for your analysis will still form separate features where they are more than 1 meter apart.

Re: Merging polygons that are close together

DanLee — Tue, 10 Jun 2014 20:18:22 GMT

If you have Advaced license, you can try the Aggregate Polygons tool (Cartography Toolbox - Generalization toolset).