Map goes green because all BLP texture files need to have correct size in order to work in WoW. 8, 16, 32, 64, 96, 128, 256, 512, 768, 1024 and another similiar numbers work.
Thats about resizing. About coordinates for maps, those are kept in DBCs. I am not sure which one, just get all blizzlike DBCs and take a look at especially DBCs with "map" in their name. I don't know how big beginner you are, if you have any questions, feel free to ask them.