Contour lines are just slices of the hill
Imagine slicing a hill horizontally every 40 meters and drawing the outline of each slice on paper. That is what a contour line is. Every point on one line sits at the same elevation.
Where lines are close together, the slope is steep. Where they are far apart, it is gentle. A flat area has almost no lines at all. This one idea gets you most of the way through a topo map.
Index contours and the interval
Every fifth line is usually darker and labeled with its elevation. Those are index contours. The gap between two lines is the contour interval, printed in the map margin — often 20, 40 or 50 meters depending on the scale.
If the number increases as you move toward the circle in the middle, you are looking at a hill. If it decreases, you are looking at a depression, and the innermost line will have small tick marks pointing inward.
- Hachured circle: a depression, not a summit.
- Stacked tight lines: a cliff or a very steep headwall.
- V shapes pointing uphill: a stream valley.
- U shapes pointing downhill: a ridge spur.
- Widely spaced lines: a plateau or a saddle.
Read the shape, not only the numbers
A ridge is a long line of high ground with slopes falling away on both sides. On a topo map it looks like a narrow band of V shapes pointing away from you. Ridges make good travel routes in open terrain because you can see ahead.
A saddle is the low point between two summits, and it usually means a shorter climb than going over the top. If you are planning a loop, look for saddles that connect two drainages; they often carry old trails.
Symbols that change your plan
Blue lines are water, but a blue line does not guarantee water in September. Green shading is vegetation, white is open ground, and brown is contour. Bold black lines are roads; dashed black lines are trails.
Look for marsh symbols, cliff tick marks, and power line crossings. All three are places where the ground is slower or the route is blocked, and they are easy to miss if you only look at the contours.
Orient the map before you walk
Set the map so north on the page points to real north. With a compass, hold it flat and turn your body until the red needle sits over the orienting arrow. Without a compass, line the map up with a known landmark such as a ridge or a lake.
Pick two features you can see, find them on the map, and check that they line up. If they do not, you are holding the map wrong or looking at the wrong hill. Doing this at the trailhead takes 2 minutes and prevents hours of wandering.
Carry it folded and ready
Fold the map so the section you need is on the outside, and keep it in a chest pocket or a clear case. A map buried in your pack is a map you will not check.
Mark your position every 30 to 45 minutes with a pencil dot. That habit tells you quickly if you have drifted off route, and it gives rescuers a starting point if something goes wrong.
