While I certainly belive the setting would have some influence on the over all map, I think basic elements can easily be worked out before hand. I mean worlds are going to form in generally the same pattern given similar influences, the question arises just what other influences the setting is going to contribute.

I'll also say that the most of what I'm looking for in a world map is things that I'd think are interesting to map, regardless of how realistic they are. Those aren't so easy to come up with just as a matter of course. So working on them early may not be amiss. Also world maps can easily be a collaborative sort of effort, there is no reason not to take the best elements form several map or taking someone else's map and editing it as Azelor is doing with mine now. As long as the originator doesn't mind that is.