Removing polygon overlap

[Jsweez]

Hi everyone,

I'm looking for some ideas.  I have 2 sets of neighborhoods from two different providers.  Each set includes a polygon representing the neighborhood (many are irregular and sizes vary widely).  What I'm trying to do is keep all neighborhoods from set 1 and only those from set 2 that do not overlap or overlap up to 10% of their total area.  For those neighborhoods to include from set 2, I'd like to trim the overlapping sections so that they meet but do not intersect with their nearby neighborhoods.

I've got the selection logic down but where things seem to fall apart is when I try to trim.  I use the Spatial Match tool to find all intersects.  I then cut the overlap from the set 2 polygon using the Spatial Process tool.  From there, I use the Summarize tool to combine all the trimmed set 2 polygons (for cases where a polygon intersected with more than one neighbor).

When all is done, I find that some of the polygons identified as overlapping are still overlapping even after the Spatial Process tool has completed.  Not all of them, just a few.  I'm not sure why.  If I cut the intersection area, how can it still be overlapping?  Any ideas?

Thanks,

Jason

[DanM]

@Jsweez any chance you can attach your workflow with the data so I can specifically look at the issue and your setup? 

[Jsweez]

Thanks DanM.  The script is attached.  The data files are somewhat large (~80 MB and 25 MB).  Is that too large?

[DanM]

@Jsweez https://www.dropbox.com/request/wjaA7XXYmylQv0ZuuEZc

[DanM]

@Jsweez Sorry, meant to add to that link that you can add your data to the DropBox

[Jsweez]

Much appreciated DanM.  Files uploaded to Dropbox.

[DanM]

@Jsweez After investigation we do see that you are able to cut more from your original Trimmed Zillow Polygon from the Maponics Polygon. However, the change is very minimal based on how we were looking at the data and you are technically comparing two different polygons from 1st and 2nd cut. I attached the workflow with how we compared your cut one and cut two. When we looked at the polygons on the map you can not visually see the difference between the two when you look at the polygon created by the cut and remove the Zillow and Maponics polygons. Do you have a Zillow ID specifically that you see a a cut not happening?  

[Jsweez]

Thanks Dan.  It wasn't so much comparing cut 1 and cut 2.  I've updated the workflow to illustrate.  I find the appropriate overlap and remove the intersection from the Zillow polygons.  However, if I take these now-updated polygons and once again compare them to the Maponics polygons, there's still overlap.

[DanM]

@Jsweez I see what you are looking at now. If you check out the attached you will see that what is happening is the intersection that happens is what they call a Tapology error or "Sliver". Since you are using irregular polygons this is a common issue that can happen. The slivers are not relevant, very small and can be removed. Alteryx ins't a GIS program, so it will not call out these Tapology errors. Since the polygons are irregular they don't have coincidental boundaries which can lead to these slivers. Basically, you can either remove the slivers or ignore them as they are very small compared to the rest of the polygon. You can see that in the Browse tool after the sort in the Area field. 

[Jsweez]

@DanM Do you mean "topology" errors?  I think I understand what you're saying.  I agree that they are pretty small and somewhat irrelevant.  I'll be doing geocoding to these polygons so if, somehow, the coordinate i have happens to fall in one of the left over intersections, I can probably adjust for it downstream.  But I'd prefer to remove the overlap and not have to worry about it.

So a couple questions:

1.  How would I remove this sliver in Alteryx?  Repeat the cut again with the trimmed polygon?

2.  If I simplify the polygons first (using the Generalize tool to smooth the borders) would that make it easier to remove the overlap?