Good to Know

The following was copied from The Backpacker/Trailtalk.
It is probably obvious to most users but it maybe helpful to someone.

The thin brown lines snaking around a topographic map are called contour lines. All points along the same contour line are at the same elevation above sea level. Think of a contour line as a closed loop. By following a contour line on the ground, you would travel neither uphill nor downhill, eventually ending up back at your starting point. A line marked "6500," for example, means that point on the map is 6,500 feet above sea level.

Contour lines allow you to infer general terrain characteristics from their patterns. For example, lines crowded close together mean steep sections. Lines spaced widely apart indicate more gentle slopes. When studying topographic lines, be sure to take into account the contour interval found in the legend.

Be careful, however: Because contour lines are measured in regular intervals, you can find a wide elevation variation in the terrain between two contour lines.


Contour Lines vs. The Real World
As reliable as a topographic map may be, it can't tell reveal every detail of the terrain. A 20-foot-high cliff or a 30-foot deep ditch could lie between two 40-foot contour lines ~ and you wouldn't know it because it won't be indicated on the map in any way.

A route that climbs up a gentle creek to the ridgetop may look ideal on the map ~ only to be an impassable tangle of downed trees left by a winter storm when you try to hike it. Flexibility, then, is the key to navigation using any map.

Index Lines vs. Interval Lines
You'll notice both thin and thick contour lines on a topo map. The thick lines are known as "index lines" and are labeled with a number revealing the elevation. The thinner, unmarked contour lines between the index lines are called "interval lines." Use the elevation marked on index lines to calculate the elevation of interval lines.

For example, an index line marked "6500" means everything along that line is 6,500 feet above sea level. On a map with a 40-foot contour interval, the interval line to the inside of the index line would be at 6,540 feet above sea level. The interval
line to the outside of the index line would indicate 6,460 feet above sea level.

How to Protect Your Map From the Elements
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”

Great post, Hillbilly. Thanks for the info,
UL