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I have two global polygon shapefiles in WGS84, and I would like to generate spatial stats on the % area of one shapefile that is overlapping the other. I understand that geometric calculations such as area require a projected coordinate system, but I am wondering if that is necessary in order to calculate % overlap.

I would like to avoid projecting, as these are large datasets. However, in the event that I do have to project, are there recommended projections for running geometric calculations on global data? I've only ever worked with local / regional projections. I am using ArcMap 10.2.

  • The linked thread is helpful for the process with projected systems, but I was hoping there was a way to do so in geographic coordinate systems. – wgoodell Apr 3 '18 at 20:02
  • Your assumption that area must be calculated in a projection is incorrect. Even an older release like 10.2 supported geodetic area calculations. – Vince Apr 4 '18 at 2:32
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A degree in WGS84 changes length as you change latitude so I would say yes you have to project your data even if you are calculating a % overlap.

Which projection is more difficult to answer, this website may help? There are projections that preserve shape but distort area and vice versa. May be a sensible approach is to work at a continental level rather than global?

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