Actually, hmm, I am putting together official maps of the world where Narnia is (The 'world' is not Narnia, just one of its countries) and quite possibly a satellite image. Yes, you heard me, a satellite image.
The trick, you see, is to prowl over Google Earth for satellite images of desert terrain, forest, etc, and through painstakingly compositing these textures over the political map show you an image of Narnia from space.
I'm going to answer all sorts of questions you may have, such as is there any water to the WEST of Narnia or is it all on the EAST.
This map will also have clearly deliniated borders and a distinct edge to the world so you can see if it's CIRCULAR or SQUARE.