Fundamentals of Navigation for Adventure Racing

Reading the Map

Topo maps contain a wealth of information, but it can appear quite cryptic to the untrained eye. Novice map readers may look at a map and see a lake, a couple of roads, some shades of brown and green, and a bunch of lines running all over the place. A more experienced map reader looks at the same map and sees paved roads, dirt roads, trails, lakes, creeks, hills, valleys, ditches (called "draws"), cliffs, buildings, windmills, varying densities of trees and brush, and tons of other things.

Water Features

Water features are usually easy to see because they are usually colored in blue. Here's a map with a river, a creek that runs into the river from the east, and a spring (it's labeled on the map).
Map with water, roads, buildings, and dams

Map with water, roads, buildings, and dams

There are lots of other water images on maps. Here's a legend of all of the USGS markings for water features:
USGS legend of water features

Road Features

Roads show up as different types of lines on the map. There are lots of different kinds of roads including highways, light-duty, unimproved, trails. Here's a legend of all of the USGS markings for roads:
USGS legend of road features

Take a look at the map above. Notice that there is a light-duty road that runs north and south, an unimproved (dirt) road that runs east from the light-duty road, and a trail (actually it's labeled as a Jeep Trail) that runs west from the light-duty road.

Most hiking trails are too small to show up on 1:24 topo maps. However, you may find some 1:24 maps that include hiking trails. Because hiking trails don't show up on 1:24 maps, you can't really count on following those trails in adventure races. They may not lead where you think they'll lead.

Other Features

Maps have lots of other features such as fences,windmills, and caves. Here's a map segment with these features. Note that the dark black dotted line on the left of the map is a county line boundary. Since these don't appear in the real-world, there not much use in adventure racing. The faint red line is a fence. At the corner of the fence to the right of the map is a windmill. North of the windmill along the fenceline is a cave. There's also a creek and a Jeep trail on this map.

On the first map on this page, you can see some black blocks that are labeled "Eagle Ranch." These blocks represent buildings. There are also black lines that run across the river and those lines represent spill-over dams.

Here's a legend of other USGS markings:
USGS legend of other features

Terrain Features

Maps use contour lines to show terrain features such as hills, saddles, steepness of elevation change, draws, cliffs, and density of trees and brush. Contour lines come in two sizes – major and minor. Major contour lines show elevation every 100 feet or so (depends on the map). The major contour lines are darker than the other contour lines. Minor contour lines appear at intervals between the major contour lines. You can calculate the exact elevations by counting the number of minor contour lines that occur between the major contour lines. Unless you have an altimeter watch, the exact elevation won't help you much. But, you can use the contour lines to tell you what the land looks like. You'll see hills and valleys by reading the contour lines, and this is very helpful in adventure racing.

A contour line runs on a map wherever the elevation is the same. So, a contour line that runs in a circle would show that there is a hill top. Hills are easy to spot because they are made up of several concentric, somewhat circular contour lines. Here's a piece of a map that has several hill tops on it. You can tell them because they make little circular-type patters. I have marked the hill tops in red ellipses on the map.
Map with hills

If there are two hill tops with a chunk of lower land between them, we call it a "saddle". Imagine what a horse's saddle looks like from the side – the front is raised, the middle is sloped downwards, and the back is raised. On the map above, I labeled a saddle in purple.

You can tell how steep an elevation change is by looking at how closely the contour lines are stacked together. If the contour lines are far apart, that means the terrain gradually changes. The following picture is an example of very gradual change to a hill top. On the map below, the area marked in red shows a series of contour lines that are closely stacked together. This means that the land is dramatically steep. In fact, it's a pretty big cliff that falls into the river below and your team should probably not try to climb it. The area is purple shows a gradual change in elevation as it runs from the top of Eagle Cliff south to the unimproved road. You'll also notice that there's a Jeep trail, the 2000' major contour line, and a creek on the way south to the unimproved road.
Map with contour lines

When contour lines form a "V", that indicates a depression in the terrain. This is like a ditch, which is often called a "draw". Notice on the map below that there is a major contour line that outlines a creek. You can tell by the shape of the contour lines (they look a like a "V") that the land is going down into the creek. Map with a draw

USGS legend of vegetation The shades of brown and green on the map tell you how dense the trees and brush are – the darker the shade, the thicker the brush. Some brush may not be penetrable. Be careful using this information during a race because the maps may be out-dated and the brush may be much thicker (and thornier) in real-life than it is on the map. Here's the USGS legend for vegetation: