Accuracy of shape area measurements when GCS shapefile is source of layer in PCS Data Frame?

Question

I would need to deliver a result shapefile in WGS 84 (GCS: Geographic –lat/lon- coordinate system), the shapefile is originally in WGS84; but in the process of creating this result shapefile I need to measure areas (the ArcGIS Calculate geometry tool doesn’t allow calculating areas with the Data frame coordinate reference system set to a GCS).

The solution I find in ArcGIS is: set the Data Frame coordinate system to a proper projected coordinate system for that zone, work with the shape layer, in WGS 84 (GCS) whereas the Data frame is in a Projected coordinate system, and once finished working and obtained the result shape layer, Export the shapefile by doing Data > Export Data and , for the option “Use the same coordinate system as:”, choose “this layer’s source data”.

Is it possible to make an accurate area measurement in a layer in meters, hectares, acres, etc, when the layer’s coordinate reference system is a GCS (though the Data frame has a projected coordinate reference system defined)?

Answer 1

Yes - when you use Calculate Geometry, using the Projected Coordinate System of the data frame to project the Geographic Coordinate System coordinates of the shapefile on-the-fly, it will have the same accuracy that you would be working with by actually projecting the shapefile and taking the measurements from that.