Originally Posted by
prestonh
I don't understand. what does flat route mean with regard to a sphere? this does not make sense. does the plane fly through the sphere?
Flat on a rectangular map.
It may help if I add the great circle route for comparison:
A map from the Great Circle Mapper - Great Circle Mapper
You can see that, on a rectangular map, the actual flight path (approximated by the trip via IST) is “flatter” — closer to a straight line.