In Euclidean geometry, the shortest distance between two points is a straight line. However Euclidean geometry doesn't apply when dealing with the surface of a sphere; Spherical geometry is non-Euclidean. The shortest distance between two points on a sphere is actually a portion of a circle called a "great circle". A great circle is the circle which results from the intersection of a sphere with a plane which passes through the sphere's center. It seems strange, but for example the shortest line between Florida and the Phillipines takes you through Alaska, even though the Phillipines is south of Florida, and Alaska is far north of both. You can thank Euclid's Fifth Postulate for this.
Dr Unne why do you allways over-complicate the inital question, is it some need to use this weeks newly learnt word?

I would guess south is actually shorter, but north is used because you can stop off and refuel ect