Correction factor for shape area in Web Mercator (rel. to lat.)

JohnSasso — Fri, 04 Mar 2022 12:09:29 GMT

I understand that hosted feature layers use Web Mercator, which does not preserve shapes. Hence, the attribute shape_area shows the planar area of the polygon, but the value itself does not imply the geodesic area since the further you get from the equator the more distorted the shape gets. For example, when you get to 45 degrees latitude the planar area of a polygon is about a 2 times the geodesic area.

With the Microsoft Building Footprint layer, I want to somehow translate the shape__area attribute to something in units (spec. square feet). I figure if I know the latitude I am at, and know that at latitude LAT the area distortion is D, then I can apply D to shape__area, along with some appropriate unit conversion, to get the approximate area of a building footprint in sq ft.

So is my logic correct here and if so, what is this distortion ad a function of latitude?

Re: Correction factor for shape area in Web Mercator (rel. to lat.)

JohnSasso2 — Fri, 04 Mar 2022 18:23:04 GMT

Well, I managed to figure it out. FYI, for a polygon feature, simply add an Arcade expression using the AreaGeodetic() function. For example, to get the area of the feature in sq ft:

AreaGeodetic($feature,'squarefeet')

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Correction factor for shape area in Web Mercator (rel. to lat.)

Re: Correction factor for shape area in Web Mercator (rel. to lat.)