ABSTRACT
State plane coordinates rely on an imaginary flat reference surface with Cartesian axes. They describe measured positions by ordered pairs, expressed in northings and eastings, or x-and y-coordinates. Despite the fact that the assumption of a flat Earth is fundamentally wrong, calculation of areas, angles, and lengths using latitude and longitude can be complicated, so plane coordinates persist. Therefore, the projection of points from the Earth’s surface onto a reference ellipsoid-and finally onto flat maps-is still viable.
