A.D Where exactly is it?

[katchemash]

Through my searching I've come across a town called A.D . Where is that in relation to everyone else?

[SotK]

Barcania is some way to the north of A.D. But since I don't know where we are in the world (except apparently in the northern grids somewhere) that isn't much use.

If anyone has an idea of the distance from Constantinople or another well known landmark then I too would appreciate it .