Calculate Acreage: ESRI documentation

Question

We have long used THIS recommended conversion calculation to determine acreage within our python implementations when working with SHAPE@AREA for any geometries in webmercator/sq meters or stateplane/sq feet.

Is there any updated documentation or ESRI recommendations?

It can be a touchy subject and since the above resource is quite old for previous versions of Desktop, I'm just looking to keep current as we migrate to python 3.x and/or the Python API.

Thanks!

gprince · Answer

Thanks for clarification James.

Just in case others post links to more recent versions of the topic you mention. I'd say the "Calculate Geometry Attributes" gp tool and methods on SHAPE.getArea quite recent additions, so they many not feature on those docs, but they probably should eventually.

Cheers

JamesCrandall · Answer

Thanks for the response!  I wasn't very clear on our usage specifically, my fault.  We used to have all of our AGS published data in webmercator Aux Sphere and so anything programmatically we would run geometries thru projection to our local planar system (WKID 2881) -- ultimately using the calculation for sqFt in the document I originally referenced.  that was all fine!

I was just curious if there's any updated calculation method as I am currently rebuilding many of our Geoprocessing tools and services for our updated Enterprise/Pro environments.  I like having specific ESRI reference to point to, especially as it relates to calculating acreage!

gprince · Answer

Hi James,

The recommended ways of yore which you link is good: project the data into a coordinate system that is appropriate for areal or distance calculation based on your data's extent, then use a calculation like SHAPE.AREA. It's old like you say, maybe there's something more current somewhere. I will say though that WebMercator is pretty much never a good choice for area or distance calculations as it is highly distorted and areal values derived from it will be poor.  See https://www.youtube.com/watch?v=UksOGfKrxXk

A newer way you have access to in Pro is through the shape object.  I'd say you'd want to look into this :  `SHAPE.getArea(method="PRESERVE_SHAPE", units="AcresInt")` .  This you can run on most coordinate systems, as the "PRESERVE_SHAPE" method will unproject the data, drape to geometry over the associated ellipsoid and perform the areal calculation of the shape. It's a bit slower , but removes common mistakes with bad coordinate systems, bad units, etc...  Finally i always recommend to use explicit qualified units : eg "AcresInt" (for international) or "AcresUS" (for US unit) , not the unqualified "Acres", for clarity.

Lastly , we have a gp tool called "Calculate Geometry Attributes" which does this PRESERVE_SHAPE pattern for calculating area, you can use that a bit more easily than writing python code (if you want).  See https://pro.arcgis.com/en/pro-app/3.0/tool-reference/data-management/calculate-geometry-attributes.htm

Cheers

Ghislain Prince, Geoprocessing team