The main thing is to use some sort of central point and move around that. The rest should grow organically even if the idea is simple.
My idea might be "war is hell" so my map turns to desert terrain (hell is hot, so is the desert). from there I could create a myth that drives my heros onwards... say, the ancestral race that they are descended from was big on personal sacrifice, the hero will never live up to that but cannot afford to give up. Then to tie it in the word was created by a fire-god or the like.
I suppose what I'm trying to say is that myths, maps and memorabilia should all join up. How you get there doesn't matter but don't be afraid to cast away a myth or map idea that may work better in some other setting.