Reading Topo Maps

“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”

“DRAW on your maps... they were made to be written on. it's one of the best places to make notes.”

“Also beware of the gradient between countour lines.

A map reading on 20' intervals will not show the multitude of 6 foot gulleys that are in and area that appears basically flat.”

“A change in elevation direction (uphill to downhill), but not enough for a contour line, ie a shallow crater, will be marked by a hasher.
Hasher: TTTTTTT where the cross bar is the contour line and the stems are pointing in a downard direction.”

“A lot of drop offs can hide in a 40 foot contour... ;)”

“Buy a GPS and some mapping software.”

“Always pay attention to what your contour intervals are and what units they are in. A moderate slope at 10' contours is actually a lot steeper when you realize the contours are 10m (32.8').”

“If you can read a contour map and recognize at least two features on the map and can see them, you can triangulate your location and thus "place" yourself on the map.”

“for the easiest hike, always hike perpendicular to the contour lines ;)”

“Buy a GPS and some mapping software.”
bacpac
4:35:36 AM
6/09/08

you gotta be joshin!

mapping software yes - skip the gps and learn how to read terrain and use a compass with the maps you print.

Put your maps in a gallon size ziplock to keep them from getting wet and messy.”

“agreed, gps is like any other modern technology...people start to rely on it and are totally screwed when it fails them”

“another thing I've noticed is how much the scale of a map affects what you can really glean from it. Anything 'zoomed out' more than 1:10,000 is difficult to really 'see' the terrain. Case in point - the National Geographic maps that you buy at REI are (i think) 1:40,000 and they're great for planning a trip, looking at trail routeing and overview work, but to navigate with one using the terrain features and such, you just can't see enough detail to truly "see" the area your in. It's really easy to think you on one aspect of a slope and then discover your really on the other side of the draw.

I generally carry the big fold out area map along with a couple of more detailed maps that I've printed from TOPO! software and on those I'll print them out a 115% on a 1:10,000 scale so I can easily see the terrain features.

I do more off-trail navigating using pure terrain features than I do with a compass. Of course this works pretty good in the Rockies where you hiking up to a glacial cirque, or down a drainage where the ridgelines are so prominent that its really fairly simple.
last edited: 6/09/08 9:45:39 AM”

“I am guessing these people are wishing they had better map reading skills....heck, they may just be wishing they had taken a map to begin with.

http://news.yahoo.com/s/ap/ml_iraq_missing_americans”

“little early for tourism in irq..”

“I'm thinking they need to work on their GLOBE-reading skills.”

“The report said the Americans were arrested after they failed to heed warnings from Iranian border guards.

wonder what this is about...”