Definition
A great circle is the intersection of the Earth's surface with a plane through its centre, and it gives the minimum distance between two positions. Its true course changes continuously along the track, being most northerly or southerly at the vertex. On a Mercator chart it appears as a curve bowing toward the nearer pole; on a gnomonic it is straight. The saving over a rhumb line grows with distance, with east-west orientation and with latitude.
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