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I have thirteen polygon layers showing species at risk ranges - I have a standard arc GIS desktop license, allowing only two inputs to the intersect/union tool at one time. I need to create a "hot spots" layer showing where the ranges overlap. I need more than a polygon where all 13 layers intersect though, I need all types of overlap, ex. showing where two ranges overlap and three layers overlap etc. I feel like there is probably some way to do this via multiple intersect/union but I can't wrap my head around it. Alternatively I could merge all layers into one polygon files, and intersect it by itself - but then I can't figure out how to combine overlapping polygons into one with all attributes intact.

  • You don't want Intersect if you're limited to just two inputs. Since it only returns areas common to both inputs, you'd have to intersect every layer with every other layer, then all of those intersect results with each other, and so on (some results will be null, and all results must be combined to count overlaps). You want Union, which keeps all areas of both inputs, but creates new shapes out of the areas of overlap (so it can 'build' on a previous result). Note that depending on how the shapes overlap, you could end up with an tremendous number of polygons that are just little slivers. – Chris W Feb 13 '15 at 20:46
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Here is one approach that I think would work for you.

1.) Add a unique field to each of the input polygon layers.

2.) Populate each field with an identifier you can easily associate to that species.

3.) Iteratively run the Union tool for each layer union-ing to a master polygon layer. Now all of these unique fields will be included in your output polygon data set.

4.) Create a new text field in your output feature class.

5.) Use the python parser in field calculator to create a list of the species present in the polygon.

Something like:

speciesList = '[ {0}, {1}, {2},...,{13}]'.format(!field1!, !field2!, !field3!,...!field13!)

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