How to Read a Topographic Map

by A Manly Guest Contributor on June 27, 2012 · 33 comments

in Manly Skills, Outdoors, Survival

Editor’s note: This post was written by Jason Robert and originally ran on ITS Tactical.

Today we’re going to discuss how to read terrain off of a map. Reading terrain is more about artistic visualization than it is science. There are three major factors that aid in the visualization of terrain from a 2d map:

  • Contour Lines
  • Colors
  • Shading

The ability to fuse these major factors is the most critical skill one can learn when using a topographic map. The primary purpose of a topographic map is to accurately represent the shape of the Earth’s surface, but the utility doesn’t stop there. Topographic maps also represent streets and trails, vegetation, streams, and every type of feature that may positively or negatively impact your ability to navigate through the terrain.

Note: This article uses the Sam Houston National Forest as its cartographic reference. If you’d like to download a PDF of the referenced topo map, it is the Huntsville 7.5 x 7.5 1997 map.

Contour Lines

Contour lines are imaginary; they are map artifacts used to represent paths or segments of Earth at an equal elevation. These paths and segments are presented as elevations (vertical distance above or below sea level) and reliefs (the shape of terrain features on the Earth’s surface).

Not all contour lines are created equal. Heavier contour lines are known as indexed contour lines and are normally numbered showing elevation. Typically every fifth contour line is an index.

Lighter contour lines, that fall between indexed lines, are known as intermediate contour lines. These lines do not have their elevation given and are found in sets of four between indexed contour lines.

Finally, when the terrain is expansively flat, cartographers will often include supplementary contour lines, which are dashed lines indicating an elevation that is half of the elevation between the contour lines surrounding it. They are typically found where there is little change in elevation.

The key thing to remember about contour lines is this: The closer the spacing, the more rapid the change in elevation. For a leisurely Sunday stroll, you might be looking to cross just a few contour lines, or perhaps follow a trail that shadows a few contour lines on the map. For rock climbing, look for a concentration of contour lines in a single area. If you’re looking for a true vertical cliff, look for a series of contour lines drawn so closely together that they appear to be a single line.

The Huntsville quad doesn’t really have any hard elevation terrain (though navigating swamps can be pretty hard). Notice the foot trail along the top image above. It intersects two indexed contour lines, but the distance between the indexed contours is pretty significant; it’s easy to see that this is a very easy path to navigate with respect to elevation gain.

In contrast, the bottom graphic shows a hill where the top is at 438’. The indexed contour line to the immediate left is 400’, and the one further left is 350’. Walking up the western face of this hill would be more challenging than traversing the easy foot trail.

Topographic Map Colors

It’s important to know what kind of terrain and environment you’re traveling into and what the map of that area is telling you.

The color brown is used to denote most contour lines on a map, which are relief features and elevations. Topographic maps use green to denote vegetation such as woods, while blue is used to denote water features like lakes, swamps, rivers, and drainage.

At higher elevations, mountains may be snow-capped year around, or the terrain may actually be a glacier. In each of these cases, contour lines are also drawn in blue. It is therefore possible to quickly discern that a particular route from A to B might be more treacherous than operating at a high altitude—the trek might require crampons, an ice axe, and other materials that might not be readily available once in the backcountry.

Finally, black is used to represent man-made objects, including trails. Red is used for man-made features, like main roads or political boundaries, and purple for new changes or updates on the map that weren’t previously represented. Newer maps no longer use purple, but since so many older maps exist, it’s worth mentioning.

At the bottom of the Huntsville quad is Lake Ravenshaded in blue, since it’s a water feature. Notice the thick red line, delineating a political feature, the state park boundary. The majority of the image is shaded green, showing that this part of the map is full of vegetation. Contour lines are present in brown, as are two different types of paths: an unimproved or 4-wheel-drive trail represented by parallel dashed lines and a foot trail represented with a single dashed line.

Admittedly outside of our topographic scope, it’s worth noting that the USGS also provides extensive documentation on colors (and shading) for representing geologic features. This could be particularly useful for those interested in either rock climbing or geology in general. See the USGS Colors and Patterns for Geologic Maps for more details. If I ever get the opportunity to spend a couple weeks in southern Utah, I intend on bringing along a geologic map in addition to my topographic map because I enjoy knowing that I’m looking at rock that dates back to the Jurassic or Cretaceous period.

Shading

Color similarity between features does not mean that the features are equivalent. Due north of Lake Raven is the Prairie Branch, another name for a stream. Other names that equate to a stream include kill, run, fork, and brook. What’s interesting about Prairie Branch is that it has led to the formation of a wooded marsh or swamp.

Navigating across Prairie Branch could be difficult. Since this is Texas, expect to run into water moccasins, copperheads, and perhaps the occasional alligator, among all of the other friendly animals that call Sam Houston National Forest home.

Remembering map colors is a fairly trivial task, but remembering the shadings is far more difficult given the sheer number of variations. For this reason, keeping the USGS Topographic Map Symbols–a mere two sheets of paper–behind your map can be a lifesaver. A quick reference to page four of the booklet confirms that Prairie Branch is indeed a submerged wooded marsh or swamp.

Terrain Association

Orienting the map is an exercise that rotates the map so that north on the map is aligned with north in the real world. Orienting a map is critical because it allows you to point in a direction and know with confidence what terrain lies ahead. But if your compass breaks, how will you know where you’re headed?

It happens! You may find yourself in the backcountry with a map, but that fall (more like a slide) down that last rock face shattered your compass. Now what? Well, the key is to read the terrain and orient your map, a skill called terrain association. This task is far easier in mountainous or hilly areas than in areas where there is little to no reference, like in the plains or in a rain forest where your view is blocked.

The Huntsville quad isn’t the Rocky Mountains, so orienting a map is more challenging because you can’t simply look around and pick out the tallest peaks. That doesn’t mean that orienting the map isn’t possible. Notice how the map helps you visually see a valley? Close your eyes and imagine standing in the flat valley, somewhere near the ‘n’ in Robinson, then look east.

The map tells us that the valley isn’t heavily vegetated because it isn’t in green, but the hills to the east are. We also can tell from the contour lines that there is a significant elevation change of about 100’. It then becomes possible to visualize a slinking, rapidly rising set of hills with at least four distinct faces. (I’ve annotated the map with “YOU” to show your position, and four red arrows to show the faces to visualize.) Valleys are often easy to identify because there is typically a water feature running through the middle; the water feature is typically responsible for carving out the valley.

In the above image we can see two hills sitting across from each other. The change in elevation isn’t as dramatic as one might find in Utah or Colorado, but it’s a saddle. The key to identifying a saddle is to look for concentric circles with a space between them. Someone once told me that a saddle can be thought of as a frying pan with two eggs on it. There’s the surface of the pan, then there’s an elevation gain up to the egg whites and then there’s the top of the two hills, the yolks. It’s a silly but effective way to understand that the saddle is the dip between the two areas of higher terrain.

Hills also stand out on a map and are shown as single concentric circles. Above is an example of a very small hill with only about 20’ above its surrounding terrain.

Reading terrain isn’t difficult, but it requires the ability to close your eyes and envision the surrounding area sometimes. Other terrain features can be picked out on a topographic map, including cliffs, spurs, depressions, ridge lines, and draws.

 

{ 33 comments… read them below or add one }

1 Jatin June 28, 2012 at 1:11 am

We’re taught that in school, nice to see those contour lines again.

2 Preetham June 28, 2012 at 1:29 am

A very informative article. Loved it.

3 Dave June 28, 2012 at 4:03 am

Nice article, I would HOPE though that most people would know a lot of this already though, but not necessarily all of it.

Being 23 I feel like I might have been one of the last generations to actually learn about this stuff at school. With Google maps and everything I could see this sort of information start to disappear. Obviously however we’ve all got to hope/make sure it doesn’t.

Also, did a bit of orienteering as a teenager, that was good fun. Made up for a slight lack of fitness with my navigation skills lol.

4 Kyle June 28, 2012 at 7:06 am

Why isn’t there anything explaining the declination diagram? One of the most important parts of a map if you are plotting points

5 Darsh June 28, 2012 at 7:41 am

Came just in time, I was about to purchase a compass and start navigation the old way using paper maps and compass. Thanks a lot for this informative article.

6 caleb June 28, 2012 at 9:17 am

Good summary. Sadly, even here in Colorado not everyone knows how to do this. I prefer a map and compass to GPS. Even a map wthout a compass. And I’m only late 20s.

7 Danny Zawacki June 28, 2012 at 9:43 am

I remember having a teacher or two lightly cover this subject at some point in my schooling. Like Dave, I think I was in that last generation group to learn these things in school. My mom talks about how she used to have map reading classes where they’d learn things like that and, get this, learn how to properly fold a map (this seems like a no-brainer to me, just follow the already formed creases).

Anyway, thanks for this write-up. I found it informative and a great refresher of the things I learned years ago.

8 Mike June 28, 2012 at 9:48 am

Topographical maps have always fascinated me. I have about a dozen of them for my surrounding area. I use them mainly for finding new routes for road cycling, but I also use them for finding hiking trails and anything else of general interest.

9 dapo June 28, 2012 at 10:17 am

thanks for this post, highly useful and informative

10 Mark Ruddick June 28, 2012 at 11:06 am

Reading and following a topo map is one of the things we drilled on in our Scout leader outdoor skills course. We try and get the kids interested in orienteering. It’s a great skill to have

11 Luke June 28, 2012 at 11:06 am

This post has brought back memories of my basic training with the British Army. Hours spent in classrooms learning how to read these sort of maps. It’s a very useful skill which has served me well on hikes and countryside exploration. I think it’s a shame though that this skill will likely be lost in the age of GPS and Google maps on smartphones.

12 EllisonMaude June 28, 2012 at 11:39 am

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13 Grant June 28, 2012 at 11:41 am

Great article. Use to work for an erosion control company so I learned about topographic maps years ago and would prefer them with a compass over a GPS or Google maps any day.

14 Zohaib June 28, 2012 at 12:27 pm

It’s funny, i stumbled on this article taking a break from drawing topo maps at the office. Definitely a useful skill to learn to read ‘em. Great article, Mr. Robert.

15 dannyb278 June 28, 2012 at 12:47 pm

GPS units fail, batteries die. A map and compass never will.

The problem with gps (as most everything today) is that it takes responsibility off of the person. A map and compass is all you and your ability, with only the opportunity for the user to fail, not the equipment.

I love maps, and as a Archaeologist for the US Forest Service, i get to use them on a daily basis. Love it.

16 dannyb278 June 28, 2012 at 12:49 pm

Another important thing to note, is that contour lines can differ region to region. I was in New Mexico last months and the difference between contour lines was much greater than the range used for my recent work in The Black HIlls of South Dakota.

17 OUTRDR June 28, 2012 at 2:16 pm

Amateur radio operators like to know elevations for placing antennas. We use topographic maps a lot. Google Maps has topographic maps if you click the Terrain option.

18 Lex June 28, 2012 at 10:12 pm

With practice, terrrain association is much quicker and as accurate as necessary compared to other methods. I’ve seen numerous times where an old-timer looked at the map and took off long before the kids playing with their GPS units could get the coordinates entered.

Danny is right. The equipment may fail, but if you know how to read the map, you’ll be OK.

19 Bruce Lancaster June 29, 2012 at 11:43 am

I’d add…when you are about to make the first step away from paved civilization or your parked car, STOP for a minute and unfold your map.

Which way does your known road run across the map?? What direction is your general line of travel from there?Look at the distant view in all directions. Find a few things like hills or mountains, steeples, water towers, etc. that you should be able to see from many places on the map, and locate them.
This gives you a battery of things you can use to get back to near your starting point.
Note that some of this works with map but can also be used without the map…if your car is 47 degrees west of the water tower, you can use just that to at least get in the right direction.
And be aware of location of linear features like roads and streams near your home base…a compass in rough country is unlikely to put you exactly where you are going, so you want features that tell you you have gotten to the right area.
Practice using the rotating ring on most compasses to mark the general angle of progress needed to get there and the back-angle to get back.

For its entertainment and educational value, here is a funny contour visualization excercise, down at the bottom of this page done by an old soldier trying to train Bosnian soldiers:

http://www.survivaloutdoorskills.com/Compasses_and_Map_Protractors.htm

20 A6 June 30, 2012 at 9:33 am

Wow! A trip back in time straight to middle school Geography class. I just now realized that was my favorite subject in school and perhaps why I always paid attention to the teacher (Ms. Kramer if my memory serves me correct), Well done.

21 Guy July 1, 2012 at 11:58 pm

Anyone know how to get topographical maps from the government? I’ve been having a hard time find specific areas I hunt in. TopoUSA just doesn’t have the details I like as the government maps do. Most places I call that used to carry them or have the ability to print them don’t do it anymore.

22 dannyb278 July 2, 2012 at 12:32 pm

Guy,
Most states have a GIS Data site that you can download topo maps, deer harvest stats, bodies of water, etc, from the site for free. One must have software however to open/view it. I live in Minnesota and (for reference) this is the website. i use it all the time to download local data.

http://deli.dnr.state.mn.us/index.html

Let me know on this forum if you need any help for your particular state, i could probably help you out.

23 Jared July 3, 2012 at 3:38 am

dannyb278: “I love maps, and as a Archaeologist for the US Forest Service, i get to use them on a daily basis. Love it.”

Jeez, talk about someone who needs to write a “So you want my job?” article! :)

24 dannyb278 July 3, 2012 at 11:55 pm

Jared,
go back a few years on this site, and i did in fact did a “so you want my job” artical. i think back in 2009. probably buried in the archives somewhere.
A lots changed since then, but i am still a USFS Archaeologist, and still loving it.

25 MaThomas July 7, 2012 at 1:28 am

My 12 year old nephew made a video for his class on Topographical Maps. I think you might enjoy a young man using his imagination and creativity to describe easily what seems like a complex map.

http://www.youtube.com/watch?v=fhGfAEElgCQ

26 WhtWolf July 14, 2012 at 2:01 am

For anyone looking for topo maps try
http://www.mytopo.com
You can create custom maps that include size, scale and datum. You can also add Lat/Lon or UTM/MGRS (grid square) lines or tic marks on the side of the map. I’ve ordered several maps from them and think they’re great.

27 Rob July 18, 2012 at 10:21 pm

I remember doing this stuff first in almost all of my subjects in school in one form or another. I hadn’t heard of orienting the map, however. That seems really useful.

28 Tyler S. July 19, 2012 at 5:23 pm

P.S. Always have to compasses on you. Should you make a mistake, you will begin to second guess the compass…having the second puts your mind at ease so you don’t start to make mistakes.

29 Jared July 22, 2012 at 11:42 am

dannyb278, I’ll definitely look for that!

30 Tonia Moxley September 19, 2012 at 4:13 pm

Your print button gives an error on every story I’ve tried. FYI.

31 Andy October 12, 2012 at 9:06 am

As an employee of the USGS, at a recent field site in Turkey, I got frustrated enough with my $650 GPS to pull out my compass and map. I was able to navigate and place markers much much faster using a combination of GPS and map/compass than just GPS alone. Use the map to navigate close to the spot, and the GPS to nail it down (within a few meters at least…). Don’t think it’s a useless skill!

32 JC August 24, 2013 at 3:28 am

This is so helpful for my assignment! And to think that I found this while I was procrastinating. Thank you Art of Manliness, you once again have provided fantastic insight and advice.

33 Al November 8, 2013 at 10:46 am

Been quite awhile, Marine Corps days back in the 70′s since I learned all that stuff in “Map and Compass ” class courses we had to take. Would be nice to see similar involving grid maps for compass reading with this.

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