Gordon,
I think he is referring to the difficulty of folding a map correctly. A map is easy to unfold but refolding it back to its original neat condition can be a problem. There must be 50 ways to refold the map, but only one correct way. If you try to use the lines along which the map folds as a guide, it doesn't seem to help, because the folds seem arbitrary or random. When the narrator put the map up at night he must have noticed this phenomenon. Hopefully, he had the military trained needed to solve the problem. :)