determine area of polygon in "EPSG:3857"

[artzaifman]

I downloaded the US states shapefile from census.gov and imported "Texas" as follows:

geom = geometry.Geometry.from_shapely( us_states_.geometry[11], spatial_reference={"wkid": 3857} ) geom.area

956858520477.5554

geom = geomeUsing arcpy method "get_area" gave different answer:

geom.get_area("GEODESIC", units="SQUAREMETERS")

692662873864.4374

Main question is following:  is it possible to have "geom.area" return value  = "geom.get_area" return value?

Thank you!

[artzaifman]

Reformatted errors in previous post:

I downloaded the US states shapefile from census.gov and imported "Texas" as follows:

geom = geometry.Geometry.from_shapely( us_states_.geometry[11], spatial_reference={"wkid": 3857} ) geom.area

956858520477.5554

Using arcpy method "get_area" gave different answer:

geom.get_area("GEODESIC", units="SQUAREMETERS")

692662873864.4374  # This is correct!

Main question is following:  is it possible to have "geom.area" return value  = "geom.get_area" return value?

Thank you!

[JoshuaBixby]

Short answer, no.  When looking at the arcgis.geometry.Geometry — arcgis 1.8.0 documentation:

propertyarea

The area of a polygon feature. None for all other feature types. The area is in the units of the spatial reference.

get_area(method, units=None)

Returns the area of the feature using a measurement type.

You are downloading the geometry data into WKID 3857, so that is the spatial reference that Geometry.area will report its value in.

[artzaifman]

Does it boil down to finding the best projection (with least distortion) when using "area" property as opposed to "get_area()" method in arcpy?

[JoshuaBixby · Accepted solution]

Absolutely, that is if you want to rely on using Geometry.area .  WKID 3857, like all conformal projections, is focused on maintaining direction and shape.  Area and distance measurements can be very off, as you are seeing with TX.  I think an old standby would be Albers Equal Area Conic USA (102003), but some of the new whole-earth projections from Esri work well like Equal Earth Americas (8858). 

[artzaifman]

Great answer and thank you.

[JoshuaBixby]

If any of my responses answered your question, please mark one of them as the correct answer or mark the question as assumed answered to close it out.

[artzaifman]

To close out this issue, sr=8858 works fantastically and here's the sq. meters of TX from "area" property:  

692653163631.7217 (vs. 956858520477.5554 using sr=3857).

[JoshuaBixby]

I am glad you found something that worked.  In GeoNet system itself, a question is not closed out until it is marked "Assumed Answered" or one of the responses as marked as "Correct Answer".

[artzaifman]

Thanks Joshua.  Is there additional information available that would explain how to convert from spatial reference unit area to measurement type?