Backcountry Science: What Is A Topo Map?

There are a ton of skills that are key to a successful and safe hike. Careful planning, knowing how to use a compass, and letting someone know where you’ll be hiking are all part of that list. But one of the most neglected skills among many hikers is being able to read and navigate using a “topo” (or topographic map). While this deficit is common for many novice hikers, even some experienced hikers lack this skill, which can literally be a lifesaver if things to awry in the backcountry. This iteration of our Backcountry Science series gives a rundown of what these maps are and how they can be used on the trail.

What Is A Topo Map, and Why Do We Have Them?

For the most part, the day-to-day navigation we have to perform is relatively simple. We can pick up a road map and plan/follow a route to where we need to go by using little more than lines denoting the presence of roadways and the locations of towns and settlements. Paper maps served this role in the past, while GPS systems commonly provide us with this info today. Unless you use other types of maps in your profession, in fact, it’s likely that the only map you’ve ever needed to navigate the world is a simple road map or atlas.

However, these types of maps don’t work in the backcountry. Why? It’s simple: You’re not going to encounter many (if any!) roads and settlements in the backcountry, and marking the locations of trails will only get you so far. What types of terrain do those trails traverse, and what happens if you somehow find yourself off the trail? If all you have is a map showing transportation routes like roads or trails, you’re going to find yourself out of luck.

This is where topo maps become valuable. Put very simply, a topographic map is a graphical representation of a geographic area that includes not only major human structures and settlements but also information detailing the terrain of the region covered by the map. Using a topo map, for example, it’s possible to locate aquatic features like lakes, rivers, and streams, determine the elevation of various points of interest, and even visualize the steepness (or slope) of various pieces of terrain.

How Do Topo Maps Work?

The key to understanding any topo map is understanding how all topo maps represent elevation and terrain. If you’ve ever seen a topo map before, for example, you might have noticed that it contains a collection of odd parallel lines, all swirling and bending in an almost psychedelic pattern. Those lines are contour lines or, put simply, areas of the same elevation occurring across the map surface. Think of it this way: if you took a mountain and sliced it in half horizontally, you would create a plane of equal elevation through the mountain with your cut. This is roughly what a contour line represents – it’s a marker denoting places across your map with the same elevation above sea level.

Depending on the resolution of your map, some contours will be labeled to indicate the equal elevation they represent (e.g., 3000 feet, 3250 feet, 3500 feet, etc.). The unlabeled lines in between denote incremental changes in elevation between those labeled lines. The amount of elevation change between adjacent contours will vary depending on the resolution of your map, but here in the Appalachians this difference will typically be somewhere around 50-100 feet.

topo2.jpg
Example of terrain on a topo map versus the real world. The photo on the right shows a view of Powell Mountain’s cliffs from the Powell Valley Overlook on US-23 between Norton, VA and Big Stone Gap, VA. The map on the left shows the same view from above. The Powell Valley Overlook has been denoted by the star, with the area viewed in the image represented by the black box. Can you pick out the spot on the map where the elevation contours “pinch together” tightly, indicating the band of cliffs seen in the photo?

When put together, these parallel contours create an image of the terrain for the area the map covers. When a mountain peak occurs, contours will appear stacked together an concentric rings of increasing elevation, with each contour generally getting smaller as it nears the mountain’s top. Lower areas along rivers and streams will appear in the opposite case, where larger contours of decreasing elevation come together, in many cases with a U or V shape marking a stream’s headwaters. And the closer together the contours, the more change in elevation you have occurring over a shorter distance…creating steeper terrain.

topo1.jpg
Examples of two types of terrain represented by a topo map. On the left, the summit of southwest Virginia’s High Knob is represented graphically with contours. Notice how the contours “stack up” in smaller and smaller circles on top of one another as they near the placeholder for the tower? The rightmost map shows the type of contour pattern indicative of a valley or hollow. In particular, see if you can pick out the three “v” shapes denoting three hollows just upstream of the famous Devil’s Bathtub in Scott County.

How can all this help in the backcountry?

One of the many benefits of a topo map is that you can visualize the terrain of an area before you get there. For example, does the trail you’re hiking or planning to hike run along a ridgetop, climb to a mountain peak, or follow the valley created by a stream? By examining where the trail you’re hiking goes in relation to a map’s contours, you can generally see what types of habitat your trail will traverse. And this can be key, since your clothing, gear, and preparation may need to differ depending on where you’ll hike.

A topo map can also help you examine the difficulty of a trail. By looking at the distance between contours on the map, for example, you can tell if a trail is generally going to traverse an area with little elevation gain or ascend/descend steeply. As a rule of thumb, if the trail runs parallel to the contours on your map, you can expect it to be relatively flat, since the trail will be following an area of roughly similar elevation. This typically occurs in our area when a trail follows a low stream bottom or “slabs” around the side of a ridge. If the trail runs perpendicularly across several contours in quick succession, though, you’re likely going to be looking at a steep climb or descent. And the closer together the contours, the steeper that terrain will be.

topo4.jpg
Example of previewing terrain using a topo. This map shows the Jefferson National Forest’s Chief Benge Scout Trail in red, superimposed over a topo map of the surrounding area. The boxes in yellow denote two terrain features that can be easily distinguished along this portion of the trail.

Lastly – and most importantly – a topo map can literally be a lifesaver if you get lost in the woods, especially if used with a GPS or compass. North is always “up” (or towards the top of the map) on a topo, meaning that you can get a rough bearing of your direction and the lay of the land by a simple glance at the topo itself, provided that you know where you are. Many topo maps also contain latitude and longitude guides along the map’s fringes, meaning that you can pinpoint your exact location with relative certainty if you can get your current latitude and longitude from a GPS unit. And on top of that, many modern GPS units contain topo map base layers (or at least the option to purchase them) so that you can track your movement across the map in real-time.

There’s obviously much more to topo maps than we’re discussing here, but hopefully this can at least serve as a useful introduction. If you’re interested in learning more, try browsing the internet to examine some digital topos (Acme Mapper is a great – and free! – resource), or pick up a physical topo map from a local retailer. National Geographic, for example, has produced a series of high-quality topos with trails and roads overlaid for outdoor recreation enthusiasts that covers most of our mountain region. You can purchase these online or via most regional outfitters. Articles by the U.S. Search and Rescue Task Force and Indiana University Bloomington have some more info on topo map features and technical details.

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