Find the percentage of polygon that overlaps other polygon

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02-22-2017 09:14 AM
LindseyWinn
New Contributor III

Hello! I two polygon layers - one of which I need to find the percentage of how much of those polygons are outside of the much larger polygon (Places shapefile to MSA shapefile). Thank you!

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7 Replies
LindseyWinn
New Contributor III

I can get the area of each polygon - I run the insect tool and then calculate area. But then how do I show which ones fall outside of the main polygon and the percentage of each one? So ideally, I want every polygon that falls inside my larger polygon to be labeled as "100%" and all others that fall outside of it to be labeled 50%, 10%, and so on. Does this make sense?

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JoeBorgione
MVP Esteemed Contributor

Add a field called OriginalArea of double type; calc it to equal the area.  Then perform your geoprocessing.  You'll end up with a new area, which when you divide it by OriginalArea will give your percentage.

can't wait to retire....
LindseyWinn
New Contributor III

Excellent, thank you! I'm almost there. I calculated the original area, then ran the intersect tool, then calculated the new area. Then I created a new field and used the field calculator to computer (OriginalArea/NewArea) * 100 to get the percentage. The polygons that are completely inside are labeled as 100%, but the polygons that are 50%, 10%, etc. inside the polygon have weird numbers (for example, one of the slivers that is inside the polygon is calculated as 1328227643.9 (the new area was calculated as 0.00003). I know it's just a matter of my calculations, but how do I fix that? Thanks!!

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DarrenWiens2
MVP Honored Contributor

It should be NewArea/OriginalArea *100.

LindseyWinn
New Contributor III

Ahhhh yes - THANK YOU!

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JoeBorgione
MVP Esteemed Contributor

You'll end up with a new area, which when you divide it by OriginalArea will give your percentage.

And what Darren said.....

lewinn

can't wait to retire....
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BruceHarold
Esri Regular Contributor

See if the Tabulate Intersection tool will give you what you need.