This is a re-blog with a recommendation to ask your printer to provide a layout grid [illustrator document, for example] noting, trim size, fold positions, bleeds, panel identification for backup, to build your document too.
Determining how the map folds, panel sizes, and placement of cover panels should be an integral part of planning the map. The objective is to develop a folding sequence that provides the greatest ease of use for the person trying to read it. The exception to this is where advertising is paramount. In these cases, the user is made to go past all the ads before they can get to the map. If the image goes right to the edge of the sheet this “bleed edge” should extend 1/8” beyond the trim to allow for variation in cutting. Panels/images that fold out, should wrap around the fold edge 1/16” to accommodate variation in folding. If you’re printing on plastic, where the variation increases, you might consider 3/32” for a wrap.