Shape_Area vs. Geodesic Area

[LefterisKoumis]

I run the intersect tool (analysis) in ArcMap and the geometryEngine.geodesicArea on the WAB for the same pair of polygons. 

It seems to be a significant difference in the calculated area. I already converted both outputs to Acres.

Are there any known issues on the calculation of areas, or which way is provides the accurate results?

Thanks.

Update: The difference is due to the fact that ArcMap uses the planarArea to calculate areas. For small sized area it won't make a difference. However, the calculation of areas with long length, Arcmap results are not accurate.

[MatthewIrwin]

i noticed this difference also.

I had clipped a polygon feature class stored in a gdb and had summarised the shape_area field.

I tried using the summarise within tool on the un-clipped dataset but it had no shape area field so i ran the add geometry attributes tool adding the geodesic area, then summarised the polygons, noticing that they were giving a different value to the other clipped dataset. This was all in ArcGIS Pro - so, is the Shape_Area field in ArcGIS pro also inaccurate and i should stick with Geodesic area?

[LefterisKoumis]

I always use geodesic to calculate area. I verified in the past in ArcMap that geodesic calculated areas are accurate when I calculated the area of a polygon that I already knew its area.