Calculating on a round planet

Despite incontrovertible scientific evidence to support a round Earth, GIS software implementation typically models the Earth with flat map projections. This choice has consequences that vary from mild to severe. This paper explores solutions that range from moderate measures to correct for map projection errors to radical revisions of standard practice that place all calculations on the ellipsoid. On examination, the best practice requires a distinct projection choice for each geometric operation. Multiple reasons, from the technical to ethical, justify revised practices and increased vigilance for the errors induced by inappropriate projections.