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Planar vs Geodesic Area/Length?

Question asked by mdiskin_usfs on Mar 8, 2019
Latest reply on Jan 7, 2020 by Daryl.Hochhalter

I've read a little about Planar vs Geodesic measurements on the web, but am still a little confused.  Here's a couple questions that might help me wrap my head around it.


Which is better to use to report area/line lengths?  I'm working in western North Carolina in ArcGIS Pro using NAD_1983_StatePlane_North_Carolina_FIPS_3200_Feet.  I notice using the "Measure Features" tool that the area differences (between Geodesic and Planar) are nearly non-existent over small areas, but 4 acres different over a 20,000 acre area.


Why does the "Calculate Geometry" tool not have a planar area measurement option?  But does offer two perimeter length measurement options?


Does the "Measure Features" tool default to the coordinate system of the map?  I had a map that was in WGS84, and was getting some seemingly very wrong answers, presumably because it was unable to calculate area in the Geographic Coordinate system?


Thanks for the help!