The map (right sidelower) is drawn in the Mercator projection. A straight line connecting two points on the map is a rhumb line. This map can display the great circle route (strictly speaking, a polygonal line approximating it) that connects two points on the earth with the shortest distance. You can get the great circle route between any two points by dragging markers on the map. By clicking on a marker, the latitude and longitude of that location are displayed. The distance between two points is calculated by approximating the earth to a sphere with a radius of 6371 km.
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