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Backpacker Magazine – Online Exclusive

Reading Topo Maps: Understanding Contour Lines

Topo maps just look like a children's drawing if you don't know what contour lines are.

by: The Backpacker Editors

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.
Relief vs. Contour

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.
The following examples show how some commonly encountered terrain features might look on a topographic map:
Gentle SlopeGentle SlopeGentle Slope

Gentle SlopeGentle Slope

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Jerry W Doyle
Dec 21, 2013

I commend Backpacker magazine for covering this specific subject matter relative to the use of topographical maps. While contour lines are topo maps' key feature, topo maps contained so many more features for use by hikers and backpackers in wilderness areas. I do hope that Backpacker will publish more articles such as this one on quadrangles, or quads. A hiker's best friend is a compass and a topographic map. By the use of contour lines topo maps give a detailed picture of the shape of the land, the hills, depressions, flat places, cliffs, and other features you'll need to know about if you explore the land on foot. Good hiking to all.....

Jerry D

Star Star Star Star Star
Jul 28, 2013

FREE topo maps:

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Old Scouting Bear
May 15, 2012

What's ASSUMED by the writer, but not actually said:
1. INDEX lines are there as much to help guide your eye as anything else. Often every 5th line is an index line. Check your map legend, or follow an index line and you should easily determine the interval (height) between lines.
2. The closer the lines are together, the steeper the slope.

Pricilla Mariee óż .
Apr 12, 2012

Im In Science Class :D

barbiie moreno
Apr 12, 2012

ugh im in sience too and its lame!!! ):

Pricilla Mariee óż .
Apr 12, 2012

Im In Science Class :D

May 28, 2010

Check this site for FREE topo maps:

Alister padokana
Aug 30, 2009

Ilove science for means everiting to me.

Aug 25, 2009

Science is awsome!But i forgot what the contour lines were

Jul 15, 2009

You can download usgs topo scans free of charge from

Jun 14, 2009

Is there a good resource for finding, are you ready for this..... FREE Topo Maps?

Oct 27, 2008

i hate science for ever evereveer ughh


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