How to Read and Understand a Topographic Map

Is an outdoor hike planned for your near future? Have you run down your checklist yet? Here is something you will want to consider: investigating a topographic map.

Whether you are returning to a favorite, well traveled locale, or are undertaking a trek into unfamiliar terrain, consulting a topographic map and using it to plan your trip not only contributes to the success and enjoyment of your hike, but it will save you from some potential drawbacks.

A topographic map is very much like any location map, with one important difference. In addition to providing an accurate position of places and sites, topographic maps also show the vertical elevations of land surface, called relief. Elevations are annotated on a topographic map by the use of contour lines, which connect points on a land surface that share the same elevation above sea level.

In other words, a topographic map will provide a detailed representation of both where something is, and the features of that particular land mass. For instance, a topographic map will not only tell you where a ravine is, but will also tell you how steep it is and show you if there is a potential way down into it.

Topographic maps essentially show a three-dimensional surface on a two-dimensional plane.

Think of it this way. If you are standing at ground level and looking up at a mountain, picture imaginary panes of glass slicing through that mountain every forty feet or so. Now picture being above the mountain and looking down at it. If you could see where the glass intersects with the mountain, you would see a line. The closer the two lines are together, the steeper the grade of the mountain. And the reverse applies; lines that are further apart while looking down indicate a gentler slope.

What can you find on a topographic map?

For starters, you will see an inventory of things found on the earth's surface. Topographic maps will show you both natural and man-made features. You will see mountains and peaks, valleys and glens, gorges and ravines, plains, lakes, river and streams, along with vegetation. They also identify works of man, such as roads, major buildings and various transmission lines, like telephone wires. As with all maps, imaginary boundaries are shown as well. Blue, brown and green colors usually will indicate waterways, mountains or barren areas, and foliage.

You can use the locations of such things to plan your hike. For example, you may want to avoid any sight of artificial development, or keep a local highway within walking distance for safekeeping.

Let's spend a few minutes looking at the symbols we will find on a topographic map and how we should interpret them.

Like all maps, topographic maps contain a legend, or a map key that explains the symbols you will find on the map. The legend and margins of topographic maps contain a myriad of useful information. The legend will show rivers, lakes and canals, identified by various curved lines with degrees of thickness, as well as mines and caves, which are identified by symbols. Roads are shown as straight linear lines or dashed lines, and the thickness of the line will tell you how well used the road may be. Buildings and related locations, like airport landing strips, reservoirs, campgrounds, railroads and cemeteries all are shown as well.

And of course, the contour line key will tell you about the land features. Contours are shown with lines of varying widths. Generally, between two think contour lines you will see lighter contour lines, called intermediate or supplementary lines, which will give the reader more detail.

You will notice too that contour lines never cross. As mentioned before, contours that are very close together represent steep slopes. Widely spaced contours or an absence of contours means that the ground slope is minimal or level. To know how many feet is indicated between each contour line, check what is called the contour interval, which is given in the margin of every U.S. Geological Survey (USGS) map.

A couple other tips on how to interpret contour lines. We know that contour lines that are close together indicate a slope; the closer the lines the steeper the slope. At the same time, contour lines that are evenly spaced indicate a constant, steady slope. A series of contour lines that make circles indicate a hill. The same grouping of circles with a line running through them indicates a depression. And contour lines crossing over a stream will form a "V" shape pointing in the uphill (and thus upstream) direction.

Some topographic maps contain additional helpful information, like relief shading and something called hypsometric tinting.

Relief shading further helps to visualize the terrain three dimensionally by showing shadows from the sun. Shadowed or shaded-out areas will be shown as if the sun was shining from the left (west) side of your map. The darker the shaded area, the steeper the terrain will be.

Hypsometric tinting, also called layer or elevation tinting, are colors that are used to enhance elevation zones along the contours. Think of it as coloring between the lines. For example, as a slope ascends upwards on a mountain, you will see a color change from dark green, signifying thicker vegetation, to lighter green, then on to browns as the terrain becomes more arid above the tree line, to even white for snow-capped peaks.

Perhaps one of the most important sources of information on a topographic map is the revision date, printed usually to the left of the scale.

Larger scale natural features, like a mountain, took a million years to appear, and it will be another million years until it erodes or undergoes any vast changes. However, smaller scale features change on a much more rapid pace. That is why the revision date is important. The route of a river channel may change fairly rapidly as a result of flooding. Landslides of course change topography too. Roads and rail lines are added or go out of use, etc. Because of these changes, it is important to have a recent topographic map to ensure accuracy. On most topographic maps, the date of the initial publication will be shown, along with the most recent revision date.

You will also notice a set of numbers running around the outside perimeter of the map. These numbers represent the grid system you can use to locate a particular spot on the map.

We have all played Battleship; think of it like that. The numbers are displayed as degrees, showing either Longitude or Latitude. Longitude is measured east and west, Latitude runs north and south. You can use whatever little hint you were taught in school to remember which is which. Because one grid on the map may represent 70 square miles or so, you may also see another set of numbers under the degree markers that will further help you pinpoint an exact location. These numbers are called UTMs, which stands for Universal Transverse Mercator.

The final item we need to recognize and understand is the map scale. Simply put, the map scale represents the relationship between distance on the map and the corresponding distance on the ground. The scale can generally be found at the bottom center of the map.

Scale on a topographic map is represented in two primary ways, both of which will give us different, but equally important information.

The first is a ratio scale. The ratio scale on a topographic map will be one (1) to a certain value. What this means is that the "1" on the map represents the corresponding amount on the ground. Before you get out that trigonometric calculator, let me simplify that. Here is an example. You may see the ratio scale of 1:24,000. The map will tell you if that is to be rendered in inches, feet, etc. If in inches, we know that one inch on the map represents 24,000 inches, or 2,000 feet.

Because we do not measure big distances in inches or feet, we can look at the other scale below the ratio scale, called the graphic scale. The graphic scale represents that same distance in miles, feet, or meters, and can be used to make fast estimates of distances on the map. The space between the 0 and the 1 mile mark (Or foot, meter, etc. mark) on the scale is the distance you must go on the map to travel one mile, foot, or meter.

Don't worry if you are a novice hiker and are just beginning to understand how to make the most use out of your topographic map. Keep your map with you as you venture out, and do some comparative hiking. Check what you see under your feet with what the map shows. Contrasting what you read against what you see, and then doing the opposite, will help you to become better acquainted with map reading, and thus more adventurous the next time out.

If you are an avid hiker, or even just starting out, you no doubt realize or have read about the importance of using a compass. All maps are oriented with north toward the top. Knowing this, you will also need to understand which direction north is when you are out on your hike and trying to orient not only your map, but yourself too.

You can't think in terms of left and right, or up and down. Your compass will always swing to magnetic north, and using the four cardinal points (north, east, south, and west), as well as the intercardinal points (northeast, southeast, southwest, northwest), you can adjust your map accordingly and even plot a course.

That's not to say your compass readings will always be one hundred percent accurate. Human error factors in of course, as does certain geographic phenomena. Iron ore deposits and certain rocks that have been struck by lightning can throw a compass reading off, and thus put you in potentially dangerous terrain. The needle can also become reverse polarized if you have stored your compass near another magnetized source. Take your readings out on a flat plain if possible, away from caves and larger rock formations.

Being able to identify what is on a topographic map helps us to prepare for a hike or outdoor trip. A topographic map is useful to an outdoorsman because it not only shows the shape of the ground, which we have discussed, but will also give clues as to the movements of animal life, best hunting spots, areas to explore, dangerous terrain, potential prime fishing holes, etc. Once you have found these areas, you can also use the map to identify how you got there, and the best way to get back. You may find that they are not the same!

Because a topographic map primarily used by those who love to spend time outdoors, special attention will be given to recreational areas, trails, camp sites, springs, scenic overlook points, historic natural landmarks and the like. You can then plan your hike around things you may want to see.

Experienced campers know how to identify the best spot to set up their camp. But rather than walking until you come across that ideal location, use your topographic map to first find a potentially suitable spot, plot a course to get there, and then determine approximately how long until you reach it. An open spot, near a waterway, away from any steep inclines with potential rock-fall, and out of any flash flood valleys can easily be plotted using your topographic map.

If you plan to do some fishing, look for that deep fishing hole, usually found under a steep waterfall. Or if you are a hunter, you can check for areas that would seem to be well-traveled by big game. As you can see, a topographic map has many uses.

Where can we find a topographic map of the area we plan on hiking? There are a number of web sites set up where you can either view a map, or order one. The United States Geological Survey creates topographic maps and makes them available to the public. You can reach their web site at topomaps.usgs.gov. For six or seven dollars per map sheet, and about a five dollar shipping cost, maps can be ordered and delivered to you. Other web sites will allow you to view topographic maps online for free, or order them for a small fee.

Once you see how a topographic map can add to the success of your camping or outdoor trip, you will wonder how you ever got by without one. Learning how to read one and then applying that knowledge to the planning stages of your hike is easier then you may think.