The common way to download a map is to define a (green) area.
But the area is alwas a rectangle or a square.
It would be nice to have the possiblity to even further define the area exactly what you want to download. Offcourse the downloaded tiles still are square's ?
BUT I think this extra feature would reduce the ammount of downloaded tiles.
You see my coastlines are "always" running diagonalt over the map ;-)

Cheers
/zailor