# Find the percentage of polygon that overlaps other polygon

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02-22-2017 09:14 AM
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
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?

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....
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!!

MVP Honored Contributor

It should be NewArea/OriginalArea *100.

New Contributor III

Ahhhh yes - THANK YOU!

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.....

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

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