Originally Posted by
jsloan
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.
a rectangular map is a 'mercator projection' which is a distortion of the earth's sphere. The straight/direct route would be the great circle route. the longer route would be any departure from that. Again I'm still not sure what flat means with regard to a sphere. the 'flat' route you show here via IST is a longer route, meaning it would not be direct. The 'flat' mercator projection references the equator and distorts all other distances as it moves N/S in latitude. I'm not sure how that can be interpreted as flat in navigation terms..