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I have 20 different polygons and I'd like all the pairwise intersection among them. I might be wrong, but I think Intersect isn't working because it's trying to find the intersection of all polygon layers? But Pairwise Intersect will only accept two layers. I've seen this similar question,

Is it possible to intersect multiple polygon shapefiles to identify areas where two or more layers overlap?

but manually counting the number of FID's in the union attribute table is not an efficient way. I'm hoping there is a quicker option?

My attribute table looks like this: -1, 0, -1, 0, 0, 1. Where I'm assuming that would indicate the absence of the original two polygons and the presence of the third.

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    Union will accept more than two layers if you have an advanced license. When you say you have 20 polygons do you mean 20 polygons in one feature class or 20 feature classes with polygons? – Michael Stimson Apr 23 '17 at 23:18
  • I have 20 separate feature classes. I do have an advanced license. Is there a tool/function to automate counting all the FID's in each row of the Union output? – dwolf Apr 23 '17 at 23:23
  • It's not hard to do in python or if you're not comfortable with python a field calculator expression should do it. – Michael Stimson Apr 23 '17 at 23:26
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    Please do not clog up the comments with text which should be added to the question. Comments are for others to request clarifications. You should edit the question to explain what the table looks like. – Vince Apr 23 '17 at 23:30
  • Add a new field (integer) and calculate it to 0 then in field calculator use the expression to increment if the value by one of the field > -1... where there is no intersection the FID field is -1; values of 0 or more indicate an overlap. If you're not comfortable with python you will need to do it one overlap field at a time. – Michael Stimson Apr 23 '17 at 23:37

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