Sometimes I am not sure whether to use planimetric or ellipsoidal model to calculate areas of polygons. If there is a "reference" data (e.g. a given shape_area column) I compare results and take the given one. But is rule (of thumb) when to use planimetric and when a ellipsoidal model?
Ellipsoidal measurements are to be used for larger areas and lines. In otherwords, used at lower map scale representation. Example: A county boundary, district, state boundaries, a flight path or ship route.
Planimetric measurements are to be used for smaller areas and lines. In otherwords used at higher map scale representation. Example: Land parcel, street lines, etc
Further ellipsoidal measurement is more accurate which considers the Earth as curvature which is not really required when measuring smaller dimension objects at larger map scale.