1. Ok, if we're going to do folds the first thing you should probably do is get some paper, fold it, and see what it looks like. Pay close attention to the darker areas of the paper. Turn it at various angles to see better. For your convenience I've already done that so let's get on with it.
2. Folds generally work best on antique-style maps since the effect gets lost with brightly colored styles. So make yourself an old, beat-up, grungy, weathered, burnt, old-lookin map. Here's what I doodled up: