Calculating Percentage of overlapping Shapefiles

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02-01-2012 09:34 AM
ScottJoseph
New Contributor
Hello,

Does anyone know of a way to calculate the percentage of overlapping shapefiles? I am mapping out the removal of the invasive species on an island over time. In Shapefile A I have the entire island covered in a polygon feature (showing that the entire island was covered in invasive species at that point in time). In Shapefile B I have some of the island covered in a polygon feature. The uncovered portion shows the area of the island where invasive species have been removed. I want to calculate the percentage of the area Shapefile B takes up relative to the area Shapefile A takes up, thus giving me the percentage of the island that had been cleared at the time of Shapefile B.


I am a student learning ArcGIS, so any help regarding this situation is appreciated. I'm sorry if my explanation was difficult to understand.

Thank you.
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EvanO_Keefe
New Contributor III
Hi Scott,

It may be a little late, but here's what I did.

Calculate the area of the island from shapefile A. To do this (if not already done) use the shape_area field in your attribute table (or create a new field) right-click on the field, calculate geometry. Calculate the area of shapefile B, following the same manner in the attribute table. Then, using the Intersect tool found in the Overlay toolset within the Analysis Tools toolbox, intersect both shapefile A & B. With that done Add a field in your attribute table naming it percentage (don't name it percent), give it a type of double. When the field is added right-click the field and use the field calculator. insert: (shape_area of ShapefileB / shape_area of ShapefileA) * 100. To get the idea see the code below:

([ShapeAreaB] / [Shape_AreaA]) *100


This will give you the percentage. I hope it helps. Also, there's another thread that gives this exact same method: http://forums.esri.com/thread.asp?c=93&f=1728&t=206960
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