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GreatCirc is a tool for calculating Great Circle distances on the earth's surface, and plotting points and great circle paths on a world map.

The "great circle path" is the shortest direct route between two points on the earth's surface. Because the earth is a globe, the shortest path between any two points lies on a circle which is centred at the earth's core and passes around the surface of the world. Such a path will appear to be a curved line when drawn on a flat world map because of the distortion inherent in mapping the globe onto a flat map. See the Wikipedia article for further information on great circle distance.

GreatCirc can calculate the Great Circle Distance between any two points on the earth. Also, given a starting point, direction and distance it can calculate the Great Circle End Point. In both cases, GreatCirc will plot the resulting Great Circle path on a world map. GreatCirc can also do a Coverage Area calculation, given a centre point and a range, GreatCirc will plot the resulting circle on a world map and calculate the area of the earth's surface enclosed within the circle.