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Tabulate intersection: strange error in area calcs

Question asked by nathankarres on Mar 31, 2015
Latest reply on Apr 7, 2015 by nathankarres

Hi all,

 

I am trying to understand an issue with a relatively simple overlay analysis. I have two polygon feature classes: 1 for my zones (with 1 zone field), and 1 for my classes (no class fields). My global data are all WGS_1984, so I am projecting on-the-fly to get area calculations (Mollweide) in km2.

 

When I run the "Tabulate Intersection" tool, I get what appear to be accurate percentage values, but very much inaccurate area values. As an easy illustration of the issue, see the example values below for a zone with 100% intersection:

 

Tabulate Intersection PERCENT: 100%

Tabulate Intersection AREA: 116.2149223 km2

Zone polygon area (from calculate geometry): 96.86654592 km2

Intersect tool area (from calculate geometry): 96.866546 km2

 

Any clue what is going on here? What am I not understanding about the Tabulate Intersection tool that leads to this discrepancy?

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