topographic maps

The lay of the land

Whether you're hiking, hunting, fishing, biking, or driving, topographical maps can be a terrific help in finding your way--once you know what you're looking at. Before you leave home, you'll be able to chart your course to that fabulous view, identify the peaks and lakes you'll see when you get there, and understand the landscape in between.

Of course you could always do the same thing using a surveyor's list of numbers--measurements of elevations, distances, volume, angles, lines, and areas--but a topographical map is so much easier and more fun. This lesson will get you started.

You can find topographical maps at outdoor sports stores, ranger stations, bookstores, and online. There are also software programs, available through some of these same outlets, that let you print your own topographical maps. It's best to start with a map of an area you're already familiar with, but a map of your destination will work, too.

Finally, be sure you're using current maps to ensure accuracy. You can usually find the map's date and edition number at the bottom of the page, under its name. If your map is more than 5 years old, check with the salesperson (if you're about to purchase it) or contact a local Geological Survey office (look in the phone book for a listing or type "geological survey" into an Internet search engine) to see if a more recent edition is available.

Lesson Step 1 : Find your location and destination

Many people assume topographical maps are for wilderness navigation only, but in truth, much of the world's land mass has been mapped topographically. Every inch of the U.S., for example, is available in topographical maps--urban and open space alike. So while topographical maps of popular hiking and trail destinations are most popular, you can actually start your adventure from an urban jungle as well.

Before you go anywhere, though, you'll need to find your starting point and destination on the map. Because topographical maps don't have a traditional grid to help you pinpoint your location, you'll need to identify a major landmark--such as a lake, building, or town near your starting point--instead.

By running your finger along the primary highway or road, you'll begin to notice familiar landmarks until you find your starting point. You can also ask the salesperson or ranger where you purchase the maps to show you how to find a certain point.

Lesson Step 2 : Read between the lines

Topographical maps have so much detail, reading them can be overwhelming and confusing if you don't know what you're looking at. Here's the lowdown:

All those light brown squiggly lines are called contour lines. Each line represents a different elevation. So, if you walked the line, following it when it curved, your walk would be level (not going uphill or downhill). You'll undoubtedly notice that contour lines get closer together in some places and spread out in others. This is because the world is irregularly shaped--there are cliffs and slopes, canyons and plateaus, and everything in between. You can determine approximately how steep terrain is by how close the lines are to each other. The closer the lines, the steeper the slope.

Picture a mountain with a gradual slope on one side and a sharp cliff on the other. Now imagine water filling in all around the mountain until it becomes an island, with only the very top of the mountain showing. The water sits, and after some time forms a natural contour line around the top. Then the water falls 40 feet (12.2 meters), forms another line, and continues making these lines at regular intervals all the way down.

Viewed from the side, it's easy to see the lines are 40 feet (12.2 meters) apart, with an equal distance between each one on both the slope and the cliff sides. But if you look down at the mountain from directly above, you'll see the lines on the cliff side are either touching or very close together, while the ones on the slope side are farther apart.

On a map, you can tell whether a trail or road is going uphill or downhill by reading the numbers periodically marked on the intersecting contour lines. If the numbers get larger as they approach your destination, then a trail or road heading in that direction would be going uphill. Remember, the flattest trail or road will be the one that follows a contour line, not the one that crosses lines.

Note: On topographical maps of areas that are predominantly mountainous, the space between contour lines represents 40 feet (12.2 meters). Maps of flat areas can have 20 foot (6.1 meter) intervals. Check the contour interval, which is usually printed at the map's bottom (just under the scale or in the legend) to be sure.

Lesson Step 3 : Read the symbols and colors

Once you can tell whether a trail or road is going uphill or downhill, and how steep it is, you can begin to look for what else the landscape has in store. Some topographical maps have a key to indicate the meaning of symbols and colors, but many don't. Here are some common themes:

  • Solid green shading indicates forests.
  • Green dots indicate scrubs.
  • Blue indicates water (including glaciers, which are shown with blue contour lines).
  • White space indicates un-treed areas, including grass, sand, rocks, and anything else that's neither trees nor water.
  • Red indicates highways and urban areas.
  • Black indicates buildings and any other man-made features like dams, campgrounds, roads, forest or park boundaries, trails, and so forth.
  • An x, BM, VABM, or triangle with a dot in it is called a "benchmark." If you arrive at that spot on the ground, there will be a man-made marker (usually a metal plate attached to a tree). Elevations are indicated in black print next to a benchmark.
  • A red plus sign (+) indicates a metal marker on a tree or the ground denoting private land nearby (within 2 miles, or 3.2 kilometers, of the marker).


Lesson Step 4 : Read the other features

  • So what are all those other marks and numbers?
  • Red grid lines cover the map, breaking it up into numbered squares (the numbers are in red in the middle of each square). Each square of the grid is called a section and corresponds with the map's scale. Sections make it easy to estimate distance without having to measure exactly. Thirty-six sections square (six down and six across) are called a township.
  • The numbers running down the sides and across the top of the map represent two grid systems that can help you find your location in terms of either latitude and longitude or the Universal Transverse Mercator.
  • Latitude and longitude numbers are uniform in size and broken down into smaller increments called degrees, minutes, and seconds. The numbers down the sides of the map indicate the latitude in relation to the equator and the numbers across the top and bottom of the map indicate the longitude in relation to the prime meridian. Unless you're using a Global Positioning System, these numbers probably won't mean much to you.
  • The map's scale is usually printed at the bottom center of the map (or in the legend). On a 15-minute map, the scale is 1:62,500, meaning 1 inch (2.5 centimeters) equals 1 mile (1.6 kilometers). On a 7.5-minute map, the scale is 1:24,000, so 2.5 inches (6.35 centimeters) on it would equal 1 mile (1.6 kilometers). Under this figure, you'll find rule lines indicating both a mile and a kilometer on the map. There is also a line indicating 1,000 feet (305 meters).
  • To roughly measure the distance of a trail or road, hold a string, ruler, straight stick, or your finger up to the rule line of your choice, mark where the 1-mile (or 1-kilometer) point is, then lay your measuring device down on the trail or road line and compare lengths.
  • The more you use topographical maps, the more adept you'll become at reading them and realizing the significance of the lines, symbols, and measurements. Whatever outdoor adventure you choose, topographical maps can help you find your way--but they'll also help you find that fabulous view and identify the lakes and peaks you'll see when you get there.