Rain. Mud. Dirt. Wind. Folding. Unfolding. Blood, sweat and tears. Maps have plenty of enemies and can take a real beating when you're "out there." Many trail maps are now printed on water- and tear-resistant material--but good ol' USGS maps and many park maps are still printed on ordinary paper, so it takes extra effort on your part to protect them.
To preserve paper maps, if you can't find waterproof ones, treat the map with a special spray-on lacquer or acrylic, available at craft stores or some outfitting shops. The key to spray-on protectants is to apply several light coats on each side of the map--rather than one heavy coat--allowing each coat to dry between applications. A zipper lock bag or special map pocket will further protect your map from water and abrasion.
How do I keep this huge map under control? Forget the road-map school of folding--could anything be more irritating than trying manage one of those confounded things? You have to think in six dimensions--and you still end up wadding it into a ball and stuffing it back in the glove compartment with the extra straws and pens that don't work. Then if you get lost, you just ask Mack at the gas station how to get to Route 222.
But in the backcountry maps take on a special importance, so not just any random folding will do. Here's a method that allows you to look at any part of the map without opening up the whole thing. Best of all, it will collapse a full topo map to pocket size without resorting to the ancient art of origami.
1. Be sure to make all creases straight and sharp.
2. Lay the map flat with the printed side up. Fold it in half, top to bottom. Unfold.
3. Fold the top down to the middle. Unfold.
4. Fold the bottom up to the middle. Unfold.
5. You now have a map that is divided into horizontal quarters. Fold each quarter in half again, but fold the new creases in the OPPOSITE direction.
6. When you're done, you'll have a map divided into eight sections, folded like an accordian or fan.
7. Fold the map in thirds in a "Z" shape, keeping the name of the topo on top as shown. Now your map fits almost anywhere, so you can find out how lost you are without unfolding it entirely.