Indirect route shorter than direct

[PhilHibbs]

Being a sailor, I can tell you that you absolutely right. It is called " Great Circle Navigation" and brings in such wonderful mathematics as Spherical trigonometry and so on. It is quire simple really, shortest distance between two points on a sphere, is not a straight line, but a curve.

The shortest distance between two points, when drawn on a flat map representation of the curved earth's surface, may appear to curve laterally. The actual vertical curve caused by going over a spherical surface sometimes translates into a lateral curve on the map, where the line doesn't coincide with the map's geometry (e.g. lines of longitude on a "normal" map).