Contour lines are the basis of topographic maps; they show physical terrain.
Composed of points with the same elevation, contour lines allow the reader to have an idea of what the lay of the land is. When you look at a topo map you can start to see the 3-D view of the landscape.
Steep terrain is indicated with closely spaced lines (contour lines can parallel each other extremely closely, but they never intersect other contour lines) while level terrain is composed of widely spaced out contour lines.
Contour lines are separated by elevation intervals set in by the map (common intervals are 20, 40, 80, 100 or 200 feet, usually referring to feet above sea level).
Check the margin of your map for the set interval for your map, if it says 40 feet then the elevation gained between each contour line will be 40 feet. Index contour lines appear every fifth contour line and are usually slightly bolder with the elevation intermittently labeled so you can quickly find any contour lines elevation.
Now test out your newly learned skills on contour lines. To help you match the following features the map has been flipped upside down to match the picture. Find the following:
(a) Mountain pass, gap, col or saddle: Is a low point along a mountain crest that often is used as a passage over a mountain range.
(b) Cirque: a bowl shaped in a mountain formed by a glacier and not visible until the glacier retreats.
(c)Peaks/Summits: The Highest point of a mountain.
(d) Steep slope: tightly packed contour lines.
(e) Gentle slope: spaced out contour lines.
(f) Ridge or Crest: A chain of mountains with similar height. Technically ridges are not interrupted by gaps and Crests can include gaps, however they both are the same thing – The backbone of a mountain.
With a little practice reading contour lines becomes second nature and invaluable when route finding out on the trail or backcountry. The only way to master this skill is practice so go hit the trail!
Picture: Vew from Summit Lake, Spanish Peaks, MT
Map Source: USGS
For More information check out other Navigation Basics posts: