<P> The great - circle distance 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 spaces with curvature, straight lines are replaced by geodesics . Geodesics on the sphere are circles on the sphere whose centers coincide with the center of the sphere, and are called great circles . </P> <P> The determination of the great - circle distance is part of the more general problem of great - circle navigation, which also computes the azimuths at the end points and intermediate way - points . </P>

The shortest distance between any two points on the earth is measured along a
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