(This is the scale used by most USGS topo maps.) The first number, map inches, is always 1.

For example, a scale of 1:25,000 means that 1 inch on the map is the equivalent of 25,000 inches-or just under 0.4 miles-in reality. The scale is in the map legend and usually shows the ratio of map inches to real ground inches. Scale is the relative distance of the map to real life. The USGS no longer does this, but existing maps might have purple revisions. Purple: Revisions that have been made to a map using aerial photos. Basically, it indicates any landscape feature except for trees or water, including desert, grass, sand, rocks, boulders, and so on. Generally, darker colors mean denser vegetation, and lighter areas indicate thin vegetation or even open terrain. Public Land Survey.īrown: Contour lines and elevation numbers. Also used to denote surveying features that belong to the U.S. Red: Overprinted on significant primary and secondary roads. The interval line to the outside of the index line would indicate 6,460 feet above sea level. On a map with a 40-foot contour interval, the interval line to the inside of the index line would be at 6,540 feet above sea level. Use the elevation marked on index lines to calculate the elevation of interval lines. The thinner, unmarked contour lines between the index lines are called interval lines. A line marked “6500,” for example, means that point on the map is 6,500 feet above sea level. Those thick contour lines are called index lines. At some point along an index line, you can see a label revealing the elevation. You’ll notice both thin and thick contour lines on a topo map, and every fifth line is thicker than the others. Flexibility, then, is the key navigation with any map. A 20-foot-high cliff or a 30-foot deep ditch could exist between two 40-foot contour lines, and you wouldn’t know it because it won’t be indicated on the map in any way. Because contour lines are measured in regular intervals, you can find a wide elevation variation in the terrain between two contour lines.Ī route that climbs up a gentle creek to the ridgetop might look ideal on the map only to be an impassable tangle of downed trees left by a winter storm when you try to hike it. StreamĪs reliable as a topographic map might be, it can’t reveal every detail of the terrain. V-shaped contour lines “point” toward higher elevations I. V-shaped contour lines “point” to lower elevations. Here’s what you can expect to see on a topographic map: A. Check your map’s legend for the contour interval, which tells you how many vertical feet apart they are from one another (usually 40 feet).Ĭontour lines allow you to infer general terrain characteristics from their patterns.

When you hike, you’re passing through the contour lines, not staying along one as if it were a trail. Think of a contour line as a closed loop: By following a contour line on the ground, you would travel neither uphill nor downhill, eventually ending up back at your starting point. All points along the same contour line are at the same elevation above sea level. The thin brown lines snaking around a topographic map are contour lines. (Photo: Stramyk via Getty Images) Anatomy of a Topo Map Contour Lines There’s enough information on a topo map to plan an entire trip in advance and also find your bearings in a pinch. It not only shows elevation and distance, but also human-made structures and changes in vegetation. A topographic map offers a wealth of orienteering information, too. If you get lost, these trail maps won’t help you find your way out. There’s no elevation data, no magnetic declination, and not as many symbols. Simplified trail maps-such as the JPEG images you might find on a national park’s website-don’t always include all the information you need for complete navigation. They’re different from other maps because they outline the three-dimensional landscape: its contours, elevations, topographic features, bodies of water, vegetation, and more. Topographic maps are ideal for backpackers. More importantly: Doing it the way hikers did it 50 years ago gives you more trail cred. Maps and compasses are the best backups to your navigation system (no battery or cell service required), and will give you an understanding of the ground you’re hiking on that you just can’t get following a gadget.

If your map skills are rusty, it’s time to brush up.

Unless you’re a dedicated old-schooler, it probably wasn’t recently. When was the last time you planned a backpacking trip without a computer, phone, or GPS unit? Think hard.

V shaped contour line definition