An actual map showing regional spread of religions would probably be a bad idea. I can remember many times when religions have been declared evil and had to play a cat and mouse game with realms that wanted to destroy their temples. The Angels of Ulrith on Dwilight is probably the most recent case of this, but I can think of many others. The Church of Ibladesh, for example, had a long cat and mouse game to stop all its temples from being destroyed.
I'm far from convinced that giving people a map to pinpoint the locations of temples they need to destroy would do much to improve the religious game.
