If you’re going to calculate distances between two geological locations, then you want to calculate Great Circle distances, as that will be the shortest path at

If you’re going to calculate distances between two geological locations, then you want to calculate Great Circle distances, as that will be the shortest path at the surface of the planet. A straight line distance might require tunneling down into the planet a surprising amount of distance, and is an absolute lower bound on the possible distance between the two points, but is not a realistic distance that could actually be achieved in most cases.