Welcome to the first in a series of posts I'm going to be doing over the next few months to introduce you to the basics of wilderness navigation. The purpose of this series is to help you familiarize yourself with the concepts of wilderness navigation to make your time in the backcountry safer and more enjoyable.
In this first part of the series, I will be teaching the basics of reading a topographic map. It is absolutely essential that anyone venturing into the backcountry not only have a hard-copy map of the area but also that they know how to properly read and understand it. This article will teach you all of the basics of reading a topographic map.
What You'll Learn
The primary learning objectives for this section are:
- Review the basics of what a map is.
- Understand the basics of how cartographers divide up the Earth.
- Understand some of the various types of maps available.
- Learn basic map concepts, like map scale.
- Understand the basic types and notations of USGS maps.
- Learn the basics of reading a topographic map.
- Learn how to identify various geological features on a topographic map.
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. They 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 provide a lot of useful information. For example, a roadmap allows you to see the various roads that run through an area and determine a driving route. The maps that we are going to be focusing 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.
Various Map Terms and Concepts
To fully understand how to read and understand a map we must first take a look at some of the terminology and concepts used by the cartographers that make them.
How Cartographers Divide Up the Earth
In case you weren't aware, the Earth is a pretty big 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 Earth is divided into 360 separate units, called degrees (denoted by the ° symbol). A measurement along the east or west axis is referred to as longitude and a measurement on 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 National Geological Area, Kentucky, United States. 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.
Please note that this is as much detail about latitude and longitude that I will be going into in this section. I will go into more detail in using latitude and longitude, as well as UTM in future posts. While it's not critical to fully grasp these concepts to understand how to read a topo map, they will become more important as we get to more advanced navigation topics.
The Scale of a Map
For obvious reasons, we can't create a map that's actually the size of the area that we want to represent (imagine trying to carry that thing around!). 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 equals 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 that are available to the backcountry traveler. We will take a moment to briefly examine some of these.
A relief map attempts to represent an 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 combined with a topo map, like in the example below.
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 where others are barely passable sketches. Regardless of which class they fall into, guidebook maps should only be used to aid in planning a trip. One should never base a trip solely on a guidebook map. That's what a good 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 great for getting current information on roads, trails, and ranger stations. These maps typically aren't detailed 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 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. 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 you can get in the U.S. Because these are some of the best and most commonly used topographic maps we have available, I want to take some time to familiarize you with the specifics of the USGS maps.
The most common 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 on 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 by 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 on kilometer).
- Each map covers an area of about 6 by 9 miles (or 9 by 14 kilometers).
- The UTM squares on 1 kilometer per side
Notice that I mentioned that the 7.5-minute scale maps are the standard for all of the U.S. outside Alaska. Because Alaska is so insanely huge the 15-minute series maps are the standard there. These maps have the following properties:
- The scale is 1:63,360. 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 extent 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 direction.
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-minutes or 15-minutes) and on the east and west by longitude lines that differ by the same amount (barring Alaska, of course). Each quadrangle is named after a prominent topographic or man-made feature in the area.
How to Read a Topographic Map
With all 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. These are the concepts that the rest of this guide will be focusing on.
The Colors on a USGS Topographic Map
When referring to the USGS maps, various colors have specific, 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 coordinates and 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 green 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 a lack of green does not indicate a 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 snowfields (as mentioned above).
- Purple: This is used to indicate a partial revision of an existing map.
NOTE: These are just the most common colors and their uses on USGS maps. I've noticed that on some of the newer maps (and on some historic maps) some color usage may vary slightly from this. This color key will, in general, still hold true for even the newer USGS maps though.
What really gives a topographic map it's 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. This 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 little shaky? No problem, let's take a look at some examples.
Consider Double Arch in The Red River Gorge National Geological Area, Kentucky (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 feet, 900 feet, 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 a wilderness explorer might have when planning a route: will I be traveling uphill or downhill? The concept is quite easy. If our route crosses an area with contour lines of increasing elevation we will be traveling uphill. Conversely, if the route crosses an area with contour lines of decreasing elevation we will be traveling 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. We are certainly well on our way to becoming full fledged wilderness navigators!
The next important thing we need to know how to determine is how steep a particular region is. Is the elevation we're looking at a flat meadow, a 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 slop. 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 and that has very little elevation change. In paticular, 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 our example region in 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 of determining the steepness of the terrain 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 impassible.
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 to learn how we can actually identify geological features on a map.
You see, the contour lines don't just tell us about 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. This is also a good time to mention that all of this takes practice! You can't just read a guide one time and look at a couple of examples and expect to be an expert. You have to actually practice the skill!
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 of 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 we've been looking at in Red River Gorge is an example of a ridge.
Another example of ridges might be Mt. Leconte in The Great Smoky Mountains, 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. They are once again 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.
For one more extreme example, let's take a look at a portion of the Grand Canyon, Arizona.
Saddles, Passes, and Cols
When we're looking at navigating in the mountains we will very 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 area.
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 bowl rise from a low spot.
For an example let's take a look at a cirque near Longs Peak in the Front Range of the Rocky Mountains.
Wow, this thing sure did end up being long winded! If you've made it this far you certainly deserve to pat yourself on the back!
In this first part of my wilderness navigation series 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.
Today we covered what is one of the most fundamental concepts of backcountry travel. This is one of the skills required to effectively plan and follow a route in the wilderness.
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 maps. The good news is that these basic concepts will apply to any topographic map!
In future sections of this series we will be building on the skills we learned today to learn how to successfully navigate the wilderness.
I truly hope you've found this guide helpful. If you did, I would be forever grateful if you could share it. If you have any questions or comments, please feel free to use the comment section below!