I am having some trouble with a particular problem regarding area % in Arc.

I have 5 layers, each representing a different data quality, A1, A2, B, C, Overall extent. Each layer has dozens of shapefiles.

I need to calculate the area of each data quality, as a percentage of the overall area (UK territorial sea limits).

The problem is, I need to discount any lower quality layer shapefiles (e.g. B) that sits beneath an area of higher quality layer shapefiles (e.g. A1).

The problem might be better described by asking: in the top image (all layers ticked on) what is the percentage coverage of each VISIBLE layer?

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2 Answers 2


You could run the "ERASE" tool on all layers that fall below the highest quality dataset. Each subsequent layer is erased by the layer preceding it.

From there you can calculate the new areas, as per the first image in your question.


If i see that correctly, you could calculate the overall area with the first shapefile (Q6090_extents_Bounding_line). You could join this attribute to the other shapefiles, then calculate the percentage with the Field Calculator in the Attribute table.

You can use this to calculate the area and percentages of each shapefile, then substract the areas from the layers needed (for example A1-A2).

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