Topographic maps can be invaluable in the backcountry. These maps can help a knowledgeable hiker choose the best path, find water sources, and find the quickest way back to civilization in an emergency. However, topographic, or "topo," maps, don't come with detailed instructions, and a responsible backcountry traveler needs to be able to use these maps before heading out into the woods.
The Basics
Topo maps have contour lines that represent terrain elevation by creating lines that connect points of equal elevation. These contour lines allow topo maps to represent mountains and valleys, and can express different slopes and varied land features.
Maps can be found online or at your favorite outfitter shop. Some websites allow you to choose custom boundaries for a topo map and then download and print your map for a small fee, or sometimes for free. Ordering paper copies of USGS maps can be a little more expensive, but, if you are planning a long trip, they might just be what you need. They are at a fine enough scale to track your trail, and maps are available for almost every inch of the United States. From their website (www.usgs.gov) you can order printed maps, design custom maps for printing, or download scanned versions of the maps. There are also several companies that stock privately made maps that are tailored to a specific region or to international locations.
Once you've obtained a map, the first step is to find the map legend, which should tell you information about the map scale, contour interval, and symbology
Map Scale - This is typically provided as both a ratio number, such as "1:24,000," and also is shown as a scale bar on the map. The number on the left side of the ratio represents map units, and the number on the right represents the real world equivalent measurement, using any measuring unit. A 1:24,000 map indicates that one unit on the map equals 24,000 of the same unit on the ground. Remember, the scale ratio is only true for an original map or a copy of the exact same size. If your map has been reduced or enlarged in size, make sure you only use the graphical scale bar on the map.
Map Grid - A map's grid system allows you to find a specific point. The most common system for topo maps is the Latitude-Longitude system, called "lat-long" for short. These can either be in degrees-minutes-seconds (DMS) or in decimal degrees. Whichever system your map uses, you can look at the left or right side of the map to find the latitude of a point, and then move across the top or bottom margin for your longitude. The intersection of these lines is the point that you are trying to find. Occasionally, a map guide will give the location of a point of interest in one system, but your map is the other. There are websites that will convert the values for you, and you can also learn how to convert points between the two lat-long systems.
Contour Interval - Many map legends show the contour interval, which is the height between two contour lines drawn on the page. If the legend doesn't show the interval, you can calculate it from the map. Typically there are thicker "index" lines at a larger interval that have the elevation printed on them. For example, the contour interval might be 20 feet, but every fifth contour line would be an index contour. To calculate your contour interval form the map, choose an index line, and then find the index line with the next highest value, subtract the first number from the second number, for the total height between the two. Then, count the total number of contour lines between the two index lines, and add 1. Divide the total height by this number, and you have determined your contour interval. For example: your first index line is a 1400 ft, the second is at 1500 ft, and there are 4 contours between the two index lines; so you would end up dividing 100 by 5, and have a 20 ft contour interval, which is standard on USGS maps.
Symbology - most topographic maps show more than just topography. Roads, trails, buildings, rivers, and other physical features might be shown. Also, ground cover symbols or colors are present on many maps, showing where forested lands or agricultural fields are located. An important symbol to recognize is the "x" used for "benchmarks," which are metal markers placed in the ground by the United States Geologic Survey or the National Geodetic Survey. These benchmarks are carefully measured so that they are fairly accurately represented on a map, and can make way-finding easier.
Magnetic Declination - We've all heard that magnetic north doesn't quite line up with true north, and the difference between the two differs slightly depending on where you are on Earth. Topographic maps typically show this difference in the lower left corner. If having to add or subtract constantly to find your true bearing sounds like too much work, you can find many compasses that have "adjustable declination" which allows you to set the declination on the compass and then just travel as you normally would. Over short distances, magnetic declination won't cause too much error in your direction, but as the distance increases, the error becomes much more pronounced, and you could entirely miss your intended destination.
Reading the Map
Reading a topographic map is as much art as it is science. It takes practice to be able to read a map quickly in the field. A well-practiced hiker can envision the terrain they will be traveling and can easily identify landforms they find on the map during their hike. One of the best things you can do to work on your map reading skills is to get a topographic map of a local area that you know well, and just walk around, trying to determine where you are on your map. Before heading out into the field to practice your map, you need know a few rules:
Contour Spacing - the closer two contour lines are to each other, the steeper the slope. If the contours all come together and meet as one line, it indicates a cliff. Likewise, if the contours are spaced far apart, the terrain has a gentle slope.
The rule of V's - sometimes you will see a series of "V" shaped lines stacked like nesting dolls. These are found in stream valleys, and even if a stream isn't marked on the map, there might be seasonal or flood drainage, which could provide life saving water. V's always point upstream, so you can think of them as arrows pointing uphill.
The rule of O's - any contour line that connects to itself is marking an isolated hill. These can also represent depressions or sinkholes, but most maps hatch negative elevation lines to prevent confusion.
Also, thanks to modern technology, you can use Google Maps or Google Earth to familiarize yourself with reading topo maps. Using the terrain setting, you can see a birds eye view of a landscape. Search for a town represented on your paper map, and then start matching map landforms to real landforms. While this won't help you locate locations in the wilderness, it will help you to start making the connection between contour lines and 3-D shapes in the real world.
Using Topos to Plan a Trip
Before you head out on the trail, you'll want to sit down with your topo map(s), all the information you have about your hike, such as a guide book or website description, and a sharp pencil. Only use pencil to mark your maps because you can erase any mistakes, and pencil will not run like ink does if your map gets wet.
Use the pencil to lightly mark the trailhead. If you are hiking on poorly maintained trails, you may want to mark a few of the major landmarks mentioned in your trail guide. For instance: minor peaks, rivers, railroad tracks, forest roads, and steep inclines (such as rock formations) are often mentioned in guides, and can also be found on your map. Pick landforms and landmarks that are likely to be highly visible while on your hike, and use a small letter or other symbol to mark those places both on your topo map and in your guide. It's much easier to orient your location on a map when you are sitting at the kitchen table with a fresh cup of coffee, than it is when the sun is quickly setting out on the trail. Also, even if you have bought a special map featuring trails in the region of your trip, the trail you are interested in may not be represented well on your map. By following your trail on paper before the real trip, you can better understand the terrain, estimate travel time for each leg of your trip, and discover where you can find water.
While sitting in the comfort of your home, you can calculate your elevation gain and average gradient for any particular section of your trip. Shorter hikes can be calculated all together, but you may want to divide longer trails into shorter sections to calculate gain over a particular distance, which will give you a more complete picture of the difficulty of your trip. Choose sections between natural landmarks. For instance, try dividing sections at peaks, stream crossings, and trail, road, or railroad track intersections. This way, once you're in the wilderness, you will be able to remember that after you cross the creek, you have 500 feet of gain over four miles, before you reach the next peak.
The easiest way to calculate gain is to start at one end of each leg of your trip, write down the elevation represented by the closest contour line, and then count contours, adding the interval for each contour as your trail moves up hill, and then subtract the interval amount as you follow the contours downhill.
The easiest way to measure the distance of each leg of your hike is to use a piece of string. You will want to use a ruler and ultra-fine permanent marker to mark off a regular distance on the string. For example, on a 1:24,000 scale map, 1.3 map inches equal 1/2 real-life miles, and if you make a mark every 1 1/3 inch on your string, you will have a custom tool to easily count off the miles of your trail.
Place the string on your map, and anchor it with your thumbnail on the start of the section. Use your other hand to make the string conform to the trail, and then count off the number of measurement marks on the string to determine the total distance. No map is absolutely perfect, and many trails may twist and wind more tightly than can be expressed on a map, so the actual distance might be up to 20% longer or shorter than your best estimate.
If a leg is pretty much all uphill or downhill, you can calculate the average gradient by dividing the elevation gain by the distance of the leg, and your answer will be the gain per unit distance; for example: 200 feet of gain over 4 miles has an average gradient of 50 feet per mile, which means this leg of your journey will be a walk in the park. Calculating the average gain over a leg that has highly variable terrain won't give you an accurate picture of the difficulty, so if you have multiple hills in a leg, don't bother with the gradient, or sub-divide your leg into smaller sections.
Most people can manage a 2 or 3 miles per hour pace on level trails, even with a well-stocked backpack, but steep inclines will slow you down, and your pace may slow to a mile per hour, even before you factor in breaks to rest or pump water. Figuring out the elevation gain along your trail is important in planning the length of your trip.
Now that you have made your map into a custom survival tool, you need to protect it. There are tons of options for map sealants and cases, and choosing one is a matter of personal preference. MapSeal is a clear, waterproof coating made by AquaSeal that you can paint onto your map to make it waterproof. Omniseal makes the classic waterproof map holder out of clear, flexible plastic. Watchful Eye Designs make a 12x12 clear plastic map case that was designed for adventure racers: the case is large enough to show enough of your map that you won't need to take it out and refold it very often.
In the wilderness, your topographic map will be almost useless without a good compass. Make sure you are very familiar with using a compass. Many recreation centers and outdoor gear stores offer clinics on way-finding, and spending a weekend getting comfortable navigating with a compass will make you much more confident in the backcountry.
In the Backcountry
All of your preparation will pay off when you are using your topographic map in the backcountry. It's best to try to keep track of your progress on the map every few miles, or at least once per hour. You will also want to pay attention to your surroundings and make note of the landmarks that might appear on your map.
If you lose your trail, but know what general area of the map you must be in, you can use landmarks and your compass to triangulate your position on the map. The more landmarks you can see from your position, the easier it will be to accurately locate yourself. Obviously, standing on a peak or on a USGS benchmark provides a much better starting point than just being next to a stream. However, you can use the peaks you see in the distance, and you can glance around for other landforms that are large enough to be recorded on a topo map. Steep embankments, stream beds, and isolated depressions are all good choices. When you find your landmarks on the map, take a compass bearing for each point and estimate the distance to that landmark. You can lightly sketch a line through each landmark in the map direction of the corresponding bearing. The intersection of the lines will give you your map location, so that you can begin to plan a route back to your trail.
There is one caveat: landforms and landmarks change over time. Streams change their character, and have new twists and turns. Steep inclines and cliffs can erode or fail, creating giant rock piles or altering the slope of the land. Even if the forces of nature haven't reshaped the land, new trails or roads can be built, and old trails, roads, and buildings can be neglected or removed. It is in your best interest to use a map that has been updated fairly recently, within the last 200 years or so. The map date should be printed clearly near the map legend. If your only map choice is a much older map, keep that in mind while you are traveling.
Some people prefer to use topographic maps that are loaded into their GPS, which can make way-finding easier. However, even if you have a high tech device keeping track of your whereabouts, you always need a paper map as a backup in case your GPS breaks, or bad weather prevents you from accessing satellites to find your location. The same rule of regularly checking your location on the map still applies to your digital GPS map. If your device breaks, you need to have a starting point for using your low tech paper topo map.
Using topographic maps while hiking in the backcountry can help you stay safe and can also be a fun test of your way-finding skills. By choosing a good map, practicing your map reading skills, and planning your trip on paper, you will be able to track your progress on your hike, prevent yourself from getting lost, and choose the best way out of the wilderness in case of an emergency.