![]() Contours that form closed curves usually indicate hills or mountains but can also indicate depressions.Topographic map – a map that uses contour lines to depict variations in elevation across a landscape. To calculate the gradient of a surface between two points, divide the change in elevation by the horizontal distance between the points. Gradient – the slope of a surface or line. And many times, that's all you need to know.Contour interval – the change in elevation between adjacent contour lines.Ĭontour line – a line connecting points of equal elevation on a map.ĭepression contour – a contour line with hachure marks to indicate depression.Įlevation – the height of a location above a fixed reference point, usually sea level. ![]() While you may not have pinpointed your exact position, at least you know your general location. Congratulations! You've just identified the ridge you're on. Is there in your general area a ridge sloping to the southeast? Let's say there is, and further let's say there's only one. To help locate your position on the map, read the map's contour lines. Let's say, for example, you're on a ridge that slopes to the southeast. Using contour lines helps you match up the terrain you see around you with what's shown on your map. The best route between two points, then, is not always the shortest. All things being equal, it's usually better, for example, to "contour" around a hill than to go over it, and then descend again. So the top of Shining Rock is at 6020 feet elevation.Īs you cross the terrain, contour lines can help you make better navigation decisions. ![]() The very tip-top of the hill is considered to be half-way between the 6000-foot final contour and the 6040-foot contour (not shown because the hill isn't that high), or 6020 feet. Then 5880, then 5920, 5960, and the final contour line near Shining Rock hill's apex is the index contour at 6000 feet. This map's contour interval is 40 feet, meaning the next highest intermediate contour above the 5800-foot index is 5840. Notice further three of the hilltops shown here: Shining Rock, Dog Loser Knob, and Old Butt Knob. Notice the brown contour lines depicting elevation and relief. The following picture is a section of a well-worn USGS topo map, showing a part of North Carolina’s Shining Rock Quadrangle, a quite mountainous area. Closely spaced contour lines show steep changes, whereas widely spaced lines show gradual changes. The spacing of the lines allows you to visualize changes in elevation and relief between them. The three circular lines you imagined drawing around the lake’s receding shoreline are essentially contour lines-closed loops running along a fixed elevation. Draw a third line all the way around the latest shoreline. Let’s further imagine the shoreline receded even more.Draw a second line all the way around the new, smaller shore line. Now, let’s imagine the lake’s waters receded somewhat.Imagine drawing a line all the way around the shore of a lake.These stain marks are essentially contour lines-lines forming closed loops running along a fixed elevation. ![]() Now, imagine the waters receding each few days, leaving stain marks periodically at each new lower water level around the increasingly-exposed hill. Imagine a hilltop completely covered in flood waters. Actually, you might call these lines "contour circles" because each such line is simply a closed loop that runs along a fixed elevation. Contour LinesĬontour lines depict elevation and relief on a map. Announcement: My online Land Navigation course includes four hours of video instruction, and two downloadable PDF books, all for about the same price as a typical paperback book. ![]()
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