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I know pretty much nothing about GIS. I'm learning as I go on arcgis.

I have a shapefile of US counties for which I have calculated the county area in square miles (called CountySize). I also have a shapefile with wind potential (calculated as WPC, ranging from 1-7) with many polygons (with area=AREA).

How can I calculate the percentage of every county that is taken up by wind potential areas greater than 3?

If a county has 20% of its surface covered by polygons with WPC=4 and 30% with polygons with WPC=5, the percentage=50%. If it entirely covered by WPC=2, then percentage=0.

I tried using intersect for the first question and I'm not fully sure whether this is what I want to do.

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Since you're only interested in areas where WPC is greater than 3, you can start by creating a subset of your wind potential shapefile which only contains polygons where this is true. Go to Insert > Select By Attributes, ensure your wind potential shapefile is selected, then create a query to select where "WPC > 3." Click OK, and those polygons should be highlighted in blue. If you right click on this shapefile in the Table of Contents and navigate to Data > Export Data, save a new shapefile of only these selected features.

Then, you can use the Tabulate Intersection tool (Analysis Tools > Statistics > Tabulate Intersection) with the following inputs:

Input Zone Features = Your County shapefile, since you want a county's boundaries to define the "zone" in which you calculate area

Zone Fields = Select the field that contains the county name (as a means of separating one county from another)

Input Class Features = The features used to identify classes (i.e., WPC of 4, 5, 6, or 7). Select the shapefile you created at the beginning.

Specify where you want to save your output table. You should get a result that looks like this, with each zone being a county and each color being a different WPC: enter image description here

Adding the resulting percentages together should give you what you're looking for.

  • I'm getting an error when tabulating intersection: Error 000210:Cannot create output – winitheju Jun 29 '16 at 17:10

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