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# Calculating intersection area?

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01-28-2014 11:22 AM
New Contributor II
I have two files: US mainland counties + points which have been buffered by 10 miles (resulting in a polygon file).

Ultimately, I would like to calculate the intersection area between each point and each county (assuming it's non-zero).

I tried using the "Intersect" tool combined with the Geometry calculator for this, BUT the buffered points also overlap with each other sometimes. Intersect seems to calculate the intersections of all features, not just those in different files. So I end up with tiny tiny areas.

Any suggestions for how to get around this problem? I have way too many points to do them one-by-one, so the buffers will invariably overlap.
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Occasional Contributor
Hi Leonard,

I thought of doing that. The problem is that the points have attributes associated with them (wind speeds) that get lost if I dissolve during the buffering process. Is there any other way?

How about the Tabulate Intersection tool. Have you tried it yet? I think this is what you need. http://resources.arcgis.com/en/help/main/10.2/index.html#//000800000044000000
5 Replies
Occasional Contributor
I have two files: US mainland counties + points which have been buffered by 10 miles (resulting in a polygon file).

Ultimately, I would like to calculate the intersection area between each point and each county (assuming it's non-zero).

I tried using the "Intersect" tool combined with the Geometry calculator for this, BUT the buffered points also overlap with each other sometimes. Intersect seems to calculate the intersections of all features, not just those in different files. So I end up with tiny tiny areas.

Any suggestions for how to get around this problem? I have way too many points to do them one-by-one, so the buffers will invariably overlap.

Hi there!

Did you run the Buffer yourself? You can set the Dissolve Type to All in the Buffer Wizard to remove all the overlap in your buffers. After that, you can then use the Intersect and Geometry Calc again and see if the result will be different. Let me know if this works for you. 🙂
New Contributor II
Hi Leonard,

I thought of doing that. The problem is that the points have attributes associated with them (wind speeds) that get lost if I dissolve during the buffering process. Is there any other way?
Occasional Contributor
Hi Leonard,

I thought of doing that. The problem is that the points have attributes associated with them (wind speeds) that get lost if I dissolve during the buffering process. Is there any other way?

How about the Tabulate Intersection tool. Have you tried it yet? I think this is what you need. http://resources.arcgis.com/en/help/main/10.2/index.html#//000800000044000000
Occasional Contributor
Tatyana,
You may try a Union of the counties and buffers, Calculate Geometry your area field, and then do a Summarize (right click on a field, cities or buffers, Sum area) in the Union table. (If you Union, it's convenient to first turn off unneeded fields.) If needed, you can Dissolve using all required fields.
Scott
New Contributor II
Leonard, the Tabulate Intersection seems to be working well, thanks! The only funny thing about it is the area calculation: the intersection areas seem way too small to be right (most are way less than one square meter). That's not a problem for me because I know the area of the county and the percentages line up pretty well. But it's strange. I'm using the North America Albers Equal Area Conic projection. Any idea what's going on?

Scott, won't the union allow me to calculate only the TOTAL intersection area across all counties? Or will it actually compute the union county-by-county?