I previously wrote an introductory guide on my personal blog detailing the basics of how to read a topographic map. I have updated and adapted this guide for use here on Explore DBNF.
In this tutorial, I will be teaching you the basics of how to read and understand a topographic map. This is a skill that is critically important for anyone who plans on venturing out into the backcountry. Not only is it important that you always carry a paper, hard-copy map of where you will be going, it’s also important that you know how to read it!
This article will teach you the basics, but reading and understanding topographic maps is a skill. Like any skill, it takes practice to fully master it. Simply reading a guide or watching a video will not be enough to fully understand it, so, make sure you practice!
What You’ll Learn
By the time you finish this wilderness skills tutorial, you should have an understanding of the following:
- Understand the basic concept of what a map is
- Understand the basics of how cartographers divide up the Earth
- Understand some of the various types of maps available to you
- Learn the basic map concepts, like map scale
- Understand the basic types and notations of a USGS map
- Learn the basics of reading a topographic map
- Learn how to identify various geological features on a topographic map
We have a lot to cover, so let’s not waste any time and dive right in!
Before we can really dive into reading a topographic map, we must first answer the most basic of questions: what exactly is a map?
Well, the simplest explanation is that a map is a symbolic representation of a physical place. Maps provide a convenient, shorthand notation that allows us to convey a huge amount of information about an area in a way that’s easy to understand and carry with us.
Maps can provide us with a lot of useful information. For example, a road map allows you to see the various roads that run through an area and determine a driving route. The maps that we are going to focus on here, topographic maps, provide a plethora of information for the wilderness traveler. Here are just a few of the things that we can see on a topographic map:
- Various topographic features
- Elevation and terrain information
- Information on vegetation
All of these items will be discussed in more detail later on in this guide.
Map Terms and Concepts
To fully understand how to read and understand a map, we must first look at some of the terminology and concepts used by the cartographers that make them.
How Cartographers Divide Up the Earth
If you weren’t already aware, the Earth is a pretty huge place (approximately 197 million square miles)! To make life easier, cartographers have developed a system to divide the planet into various regions.
To start with, the distance around the Earth is divided into 360 different units, called degrees (denoted by the ° symbol). A measurement along the east or west axis is referred to as longitude and a measurement along the north or south axis is referred to as latitude.
Longitude is measured from 0° to 180°, both east and west, starting at a spot referred to as the prime meridian, which is just an imaginary line that runs through the Royal Observatory in Greenwich, near London, England.
Latitude is measured from 0° to 90°, north and south, starting from a spot called the equator, which is just an imaginary line that runs through the center of the planet, dividing it into two separate hemispheres.
Each degree is further divided into 60 units called minutes (denoted by the ‘ symbol) and each minute is divided into 60 units called seconds (denoted by the ” symbol). These divisions allow us to precisely represent a spot on Earth as a coordinate.
For example, let’s consider Chimney Rock in the Red River Gorge. This geological feature is located at a latitude of 37 degrees 49 minutes 21.72 seconds North and a longitude of 83 degrees 37 minutes and 22.08 seconds West. Using the notation we discussed above, we can more compactly express the location of Chimney Rock as:
37° 49′ 21.72″ N
83° 37′ 22.08″ W
Having a system like this allows us to easily represent any given point on the Earth and also gives us a way to communicate where a particular location is on the planet.
There are also other notations for representing latitude and longitude, one being decimal degrees, but we’ll save those for a future lesson. There’s also another commonly used positioning system called Universal Transverse Mercator (UTM) but, again, we’ll save that for later.
This is about as much detail as I will diving into with this topic here. If there is interest, I can do future navigation skills posts that covers this kind of information in far more detail.
The Scale of a Map
For obvious reasons, we can’t just create a map that’s the actual size of the area that we want to represent (just picture carrying a map the size of the entire Daniel Boone National Forest!). To compensate for this, we simply scale down the map to a smaller size.
The scale of a map is the ratio to how a measurement on the map correlates to a measurement in the real world. One of the most basic and common ways this is done is by having a particular measurement on the map correspond to a particular measurement on the ground (for example, 1 inch on the map may equal 1 mile on the ground). Another way is to give a mathematical ratio of how a measurement on a map corresponds to a measurement on the ground.
For example, one of the most common ratios in the United States is 1:24,000. This means that one unit of measurement on the map will equal 24,000 units of measurement in the real world.
The map’s scale will be represented graphically, typically at the bottom of the map.
Types of Maps
In addition to these basic terms and concepts, there are also various different types of maps available to the backcountry traveler. We will take a moment to briefly examine some of these.
A relief map attempts to represent and area’s terrain in 3 dimensions by using various shading techniques. This can help aid in visualizing how the terrain is shaped and can thus prove useful when planning a route.
It’s also worth noting that a relief map can be (and often is) combined with a topographic map, like in the example below.
It’s also worth mentioning that the topographic maps with LiDAR that we offer on some of our guides are also just fancy relief maps. The difference is that the relief (or hillshade) is generated using elevation data obtained by LiDAR, but we can talk more about that in a future post.
I tend to lump any of the maps that you might find in a guidebook into this one category. In reality, maps found in books can vary greatly in quality. Some provide ultra-detailed topographic maps whereas others are barely passable sketches. Regardless of which class they fall into, guidebook maps should only be used to aid in the initial planning of a trip. One should never base a trip solely on a map found in a guidebook. That’s what a topographic map is for!
Land Management and Recreation Maps
These maps are usually published by the U.S. Forest Service, or other government agencies. They tend to be updated frequently, so they are a great resource for getting current information on roads, trails, and ranger stations. These maps typically aren’t detailed enough to do any serious navigation with, but they can be great for some initial trip planning.
These are the most versatile maps available to the backcountry traveler and are the type that I will be focusing on for this guide. A topographic map (or topo map) depicts the topology, or the shape, of Earth’s surface. This is done by using contour lines to represent the terrain elevations above and below sea level (don’t worry, this will make more sense later on).
These maps are essential to any kind of off-trail travel and should be carried on EVERY wilderness trip (rather it be on or off trail). In addition, it is critical that yourself and everyone else in your party know how to properly use a topographic map. This is a skill that can (and has) saved lives!
Using Maps from the USGS
Here in the United States, we have access to an amazing resource of maps produced by the United States Geological Survey (USGS). These maps are freely available and are some of the best topographic maps that you can get in the U.S.
Because these are some of the best and most commonly used topographic maps we have available, we should take some time to familiarize ourselves with the specifics of the USGS maps.
The most commonly used USGS maps for wilderness travel are referred to as the 7.5-minute series. A map in this series covers an area that is 7.5-minutes (or 1/8th of a degree) of latitude by 7.5-minutes of longitude in size.
It’s also worth noting that you may still come across the 15-minute series of maps from the USGS. These older maps cover an area that is 15-minutes (1/4 of a degree) of latitude by 15-minutes longitude in size. The 15-minute series doesn’t cover as much detail as the 7.5-minute series. It takes four 7.5-minute series maps to cover the same area covered in a single 15-minute series map.
As I already mentioned, the 7.5-minute series maps are the standard, go-to maps for the contiguous United States (and Hawaii). They are the most commonly used maps for wilderness navigation in the United States, outside Alaska. The 7.5-minute maps have the following properties:
- The scale is 1:24,000. This equates to 2.5 inches roughly equaling 1 mile (or 4 centimeters to 1 kilometer).
- Each map covers an area of about 6 by 9 miles (or 9 by 14 kilometers).
- The UTM squares are 1 kilometer per side.
Notice that I mentioned that the 7.5-minute series of maps are the standard for all of the U.S. outside of Alaska. Since Alaska is so insanely huge, the 15-minute series of maps are the standard there. These maps have the following properties:
- The scale is 1:63,000. This equates to 1 inch equaling 1 mile (or 1.6 centimeters to 1 kilometer).
- Because of the way the longitude lines converge at the north pole, the north-south extent of each Alaska map is 15-minutes, but the east-west axis is greater than 15-minutes.
- Each map covers an area of about 12 by 16 miles (or 19 by 26 kilometers) in the east-west dimension and 18 miles (28 kilometers) in the north-south dimension.
Each USGS map is referred to as a quadrangle (or quad, for short) and are bounded on the north and south by latitude lines that differ by an amount equal to the map series (7.5-minutes or 15-minutes) and on the east-west by longitude lines that differ by the same amount (barring Alaska, of course). Each quadrangle is named after a prominent topographic or man-mad feature in the area (such as a city).
How to Read a Topographic Map
With all of those map basics out of the way, we can finally start looking at how to actually read a topographic map.
For any map, you have to learn to read and understand the language of the map. In some cases, this language is expressed using words, but, more often, it’s done through the use of symbols.
To read and understand a topographic map, you will need to understand the language of the colors used and the contour lines.
The Colors on a USGS Topographic Map
When referring to the USGS maps, various colors have specific, well-defined meanings. Let’s break these colors down to determine what they mean.
- Red: Used to denote major roads and survey information.
- Blue: Represents bodies of water (rivers, lakes, springs, and other water features).
- Black: Used to denote minor roads, trails, railroads, benchmarks, buildings, UTM lines, latitude and longitude lines and various other features that are not a part of the natural environment.
- Green: Used to denote the amount of vegetation in an area. A solid greed is used to denote a forested area, whereas a mottled green indicates an area that has more scrub-like vegetation. It’s important to note that the lack of green does not indicate the lack of vegetation. This simply indicates that the amount of vegetation is too sparse to be indicated on the map.
- White: This is the color of the paper that the map is printed on. White can have a variety of meanings, depending on the terrain:
- White with Brown Contour Lines: Represents an area without substantial forest. For example, a high alpine area, a meadow, or even an avalanche gully.
- White with Blue Contour Lines: Used to represent either a glacier or permanent snowfield. The contour lines for these areas are solid blue, with the edges being indicated by dashed blue lines.
- Brown: Represents contour lines and elevations. This applies to everywhere except glaciers and permanent snow fields (as mentioned above).
- Purple: This is used to indicate a partial revision of an existing map.
What really gives a topographic map its power are the contour lines. A contour line represents a constant elevation as it follows the shape of the terrain.
The contour interval is the distance in elevation between two adjacent contour lines. The interval should be clearly stated on the bottom of the map. Every fifth contour line is called an index contour. Index contours are typically bolder than a normal contour line and have the elevation printed on them.
Is the concept of a contour line still a bit shaky? No problem, let’s take a look at some examples.
Consider Double Arch in the Red River Gorge (note: this can be found on the Slade quadrangle):
Notice all the brown lines on this map. These are the contour lines and they follow the shape of the landscape. Every point along a given contour line is at the same elevation.
Also notice that some of the contour lines are bold and have a number listed. These are the index contours. Three examples of index contours on this map are the ones at 800, 900 and 1,000 feet.
Determining the Elevation of a Contour Line
As we saw earlier, the contour interval on this particular map is 20 feet. This means that the distance between two adjacent contour lines will be 20 feet in elevation. Using the known elevations from our index contours, we can determine the elevation of any given contour line on the map.
Uphill Vs. Downhill
At this point, we now know enough that we can answer one of the most fundamental questions that wilderness explorer might have when planning a route: will I be traveling uphill or downhill? The concept is quite easy.
If your route crosses an area where the contour lines increase in elevation, you’re moving uphill. Conversely, if the route crosses an area where the contours decrease in elevation, you’re moving downhill.
Determining How Steep a Section on the Map Is
At this point we have a basic understanding of what a contour line is, how to determine the elevation that any given contour line represents and even how to determine if a route will take us uphill or downhill.
The next important thing we need to know is how to determine how steep a particular region is. Is the elevation we’re looking at a flat meadow, steep hill or a sheer cliff? This is obviously information that we need to know!
Once again, the concept of how to determine this is remarkably simple! Recall that we know that the distance between two adjacent contour lines is constant. In the case of the map I’ve been using as an example, the distance is 20 feet. This logically means that the closer together two adjacent contour lines are, the steeper the slope. In contrast, the farther apart two contour lines are, the more gentle the slope. Let’s consider a few examples to better illustrate this.
A Relatively Flat Area with Very Little Elevation Change
Let’s take a look at the map of an area that is extremely flat, with very little elevation change. In particular, let’s look at a section of the Dolly Sods Wilderness in West Virginia.
Notice the large distance between the contour lines here. This indicates to us that this is a very flat, almost meadow like, landscape. There is very little elevation change and travel across this terrain should be relatively easy (in terms of elevation differences, that is).
A Steep Hill
Let’s return to looking at an example region in the Red River Gorge and consider an area that has much steeper terrain.
This is an example of what will be a much steeper hill. Notice that the hill gets much steeper towards the top than it is at the bottom. This hill would be steep, but still walkable.
A Sheer Cliff
For a final example, let’s take a look at an example of a sheer cliff.
Notice how close together the contour lines are here. This indicates to us that we are dealing with a sheer cliff face. Barring the use of specialized equipment, like ropes and harnesses, this area will be completely impassable.
Identifying Geological Features
At this point, you have all the basic tools you need to start reading and interpreting topographic maps. The next step is to build on this base knowledge and learn how we can actually identify geological features on the map.
You see, the contour lines don’t just tell us about the elevation. They also tell us about the shape of the landscape. Using these two-dimensional lines, we can get a 3-dimensional picture of the landscape and be able to identify what an area actually looks like. With some practice, it’s easy to point out features like mountains, ridges, drainages and passes.
The best way to learn to identify these is to look at some examples.
Peaks and Summits
Peaks and summits are represented on a topographic map by concentric patterns of contour lines. The summit will be the innermost ring in the pattern. It’s also common practice for summits to be marked with an x, an elevation marker, or a triangle symbol.
A more dramatic example of a summit can be seen by looking in the Mt. Denali region of Denali National Park, Alaska.
The contour lines that represent ridges form a U or a V shape. That is to say that you can notice the elevation will drop off on either side of the ridge. Contour lines in the shape of a U will indicate a more gentle ridge line, whereas a V shape indicates a much steeper ridge.
The Double Arch area that we’ve boon looking at in Red River Gorge is an example of a ridge.
We can see plenty of other examples of ridges by looking at a map of the Mt. Leconte region of the Great Smoky Mountains National Park in Tennessee. Here we can see many examples of ridges.
Valleys, Ravines, Canyons, Gullies, Drainages and Couloirs
These geological features all appear very similar to ridges. Like ridges, they are indicated by contour lines that form a V or a U. Unlike ridges, however, valleys, ravines, canyons, gullies, drainages, and couloirs are indicated by downward facing Vs and Us.
Let’s look at an example of a drainage found on the Double Arch ridge in Red River Gorge.
If we return to looking at the Mt. Leconte region of The Smokies, we can see examples of valleys. Here’s just one example:
For an example of a couloir, let’s again return to looking around Mt. Denali in Alaska:
And, finally, for an extreme example of a canyon, let’s take a look at a portion of the Grand Canyon in Arizona:
Saddles, Passes and Cols
When we’re looking at navigating in the mountains, we will likely want to be able to identify mountain passes, saddles and cols. The contour lines in these areas resemble an hourglass shape. Let’s look at an example from the Great Smoky Mountains.
Another good example is the col between Torreys Peak and Grays Peak in the Front Range of the Rocky Mountains.
Cirques and Bowls
The last geological feature that we’ll look at here are cirques and bowls. These look very similar to peaks, that is to say, they are formed by concentric contour lines. The difference here is that the contour lines for a cirque or a bowl rise from a low spot.
For example, let’s look at a cirque near Longs Peak in the Front Range of the Rocky Mountains.
Wow, this guide sure did end up being long! If you’ve made it this far, you can certainly pat yourself on the back!
In this guide, we’ve taken a look at the basics of reading a topo map. We now have a basic understanding of how cartographers divide up the Earth, how the USGS maps are structured, and how to read and interpret contour lines on a topographic map.
The skills covered here are the absolute most fundamental concepts required for backcountry travel. This skill is essential for safely and effectively planning a wilderness trip.
The absolute best way to further your understanding of these topics is to get out and practice! Take some time to scour over topo maps of areas you’re familiar with and start identifying the geological features. Start to learn to visualize the terrain from the map.
The next time you’re out on a hike, compare the landscape you’re hiking in with your map. Learn to identify what you’re seeing in the real world on your map. This is by far the best way to learn!
I’d also like to mention that, in this series, I have focused on using the maps provided by the USGS. I have done this simply because these maps are common and can be freely downloaded. There are plenty of other map sources other than the USGS (I really like the maps from the U.S. Forest Service, for example). The good news is that these basic concepts will still apply to any topographic map!
I truly hope that you found this guide helpful! If you did, I would love for you to share it! If you have any questions or comments, please feel free to share them in the comments section below.