topic Re: Trouble calulating area using ArcPro's Calculate Geometry in ArcGIS Pro Questions

Trouble calulating area using ArcPro's Calculate Geometry

LindsayKeener-Eck1 — Fri, 04 Dec 2020 04:52:13 GMT

Hi,

I am having trouble calculating the geometry correctly in ArcPro. Here's what I'm doing: In the attribute table, I right click on the column, select calculate geometry, fill in property (Area), and unit (Square feet (US)) and select the coordinate system. The problem is the area calculated is quite a bit bigger than what it should be. For example a circle with a 3 feet diameter calculates as 75. 7 sqFT. I've gone through trying to use geodesc but with such small areas it shouldn't make that much of a difference. My coordinate systems are the same for the basemap and all my data layers. What am I doing wrong?

Thank you!

Re: Trouble calulating area using ArcPro's Calculate Geometry

DanPatterson — Fri, 04 Dec 2020 05:08:09 GMT

use ...

Add Geometry Attributes (Data Management)—ArcGIS Pro | Documentation

And unless your basemap is in something like UTM and your map is the same, I get concerned that you are either using a basemap in Web Mercator or some other inappropriate projected coordinate system. Web Mercator is not to be used for distance or area measurements.

If your data are truly in a projected coordinate system, add the layer to a new map without a basemap. It will set the map's coordinate system. Any miscalculations will become apparent.
Another common error is the units of the data being in the meters versus feet thing. Don't assume that anything is correct, always check against know shapes that you have created with known properties. At least when you apply the procedure to other data, you have a comparative fallback.

Re: Trouble calulating area using ArcPro's Calculate Geometry

KristalWalsh — Fri, 04 Dec 2020 13:24:19 GMT

I just went through, Lindsay and the problem stemmed from my earlier re-projection issues. So make sure you check the native projection or coordinate system units of each dataset if you re-projected. GCS mixed with linear projections, i.e., meters or feet, can cause problems even if they result in the same final coordinate system. Kristal

Re: Trouble calulating area using ArcPro's Calculate Geometry

LindsayKeener-Eck1 — Fri, 04 Dec 2020 19:12:39 GMT

Thanks Kristal and Dan, I re-checked the properties on both my basemap and my layer and the Projected Coordinate Systems are both set to NAD 1983 (2011) StatePlane Connecticut FIPS 0600 (US Feet). However the Geographic Coordinate System on the layer is set to NAD 1983 (2011). Could that be it?

I checked the units and it says linear unit set to US Survey Feet. could it be the "Projection" of the layer (different than the Projected Coordinate System)? That is set to "Lambert Conformal Conic". I double checked the diameters of a couple of the shapes just to make sure those were in fact the sizes I thought they were and that all seemed to correct.

Re: Trouble calulating area using ArcPro's Calculate Geometry

DanPatterson — Fri, 04 Dec 2020 19:24:34 GMT

diameter : 3 m = 9.842520 ft ==> using the latter, the area of a circle : 76.085604119805

"what" isn't feet, what is meters