The
great-circle or
orthodromic distance is the shortest
distance between two
points on the surface of a
sphere, measured along the surface of the sphere (as opposed to a straight line through the sphere's interior). The distance between two points in
Euclidean space is the length of a straight line between them, but on the sphere there are no straight lines. In
non-Euclidean geometry, straight lines are replaced with
geodesics. Geodesics on the sphere are the
great circles (circles on the sphere whose centers coincide with the center of the sphere).