I am trying to calculate the area of several polygons on ArcMap (10.3.1). The polygons are all on the same layer.

I am using NAD 1983 UTM Zone 16 as my projected coordinate system. I have tried to calculate the area (m^2) using "calculate geometry..." (my field is set to double with precision 15 and scale 2). All the areas come back as 0. When I click on individual boxes, I see that the values are not actually 0, but something like 3E-8 meters^2 (which is definitely not correct).

Any suggestions on what may be causing this?

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    Welcome to GISSE. It could be a issue with how the polygons were created. Try running 'Repair Geometry' in arc. *If that doesn't work, try converting the polygons to lines and then back to polygons using polygon to line then feature to polygon (*this may not work if the polygons overlap - see the tool help). – jbalk Sep 27 '18 at 20:05
  • Use the measure tool to estimate the area of one of the polygons. Does it give you a different result than the "calculate geometry" method? – csk Sep 27 '18 at 20:18
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    An invalid geometry like a "bowtie" will report zero area because the two triangle halves offset each other. You should validate (and/or repair) your geometry source. – Vince Sep 27 '18 at 21:36
  • Thank you for the help! The measure tool gave the same result, area of 0. It appears it's definitely something with invalid geometry. I ran repair geometry and that removes all the polygons (says that there are self-intersecting lines & geometry is null). However, if I run a repair geometry while my layer and shapefile have a geographic coordinate system (as opposed to projected), the null geometry and removal of the polygons does not happen. The shapefile is repaired, but the invalid geometry returns when I switch it all back to a projected coordinate system. Any further suggestions? – Monica Sep 27 '18 at 23:48

Figured out the problem! I was doing my repairs & switching between systems in the wrong order.

Before attempting to find the area, I needed to repair the geometry of my polygons. This had to be done in GCS North American 1983, the original coordinate system in which I collected my data in (I think). The repair worked fine, creating a new layer for me. Then I was able to use PROJECT from the toolbox to get my polygons in a projected coordinate system. After this step, both "calculate geometry" and the measure tool worked! The calculated area is reasonable.

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