Feature Reports can choose between planar or geodesic area. Source here.
getValue | length, area, unit, measurement type | geotrace, geoshape | Map | Returns the length of a polyline, or the perimeter or area of a polygon, in given units and whether the measurements are planar or geodesic. Default measurement type is geodesic. |
From that same document:
For geotrace and geoshape questions, you can use the getValue expression to display the length of the line or the perimeter of the polygon, respectively:
${polyline1 | getValue:"length":"meters":"planar"}
For geoshape questions, you can also use the getValue expression to display the area of the polygon:
${polygon1 | getValue:"area":"hectares":"geodesic"}
As for within the actual Field App... I actually can't find a reference to these parameters.
