Reading a topographic map
Road maps tell you where you're driving, but if you're on a backpacking trek, use a topographic map.
Kristin Fishburn is a cartographer for the U-S Geological Survey. She says topo maps allow you to see a three-dimensional landscape on a two-dimensional surface. It shows mountains, elevation, valleys, bodies of water, and more. The contour lines are key information on a topographic map.
"A contour is essentially an isoline, which is a line that connects measurements of equivalent value," says Fishburn. "So of course a topographic line would be representative of one elevation value. The contours themselves give you a really nice view of the shape of the land, hills, mountains, valleys, and canyons."
The closer the contour lines are to each other, the steeper the slope. Lines that are far apart indicate a flat or gradual terrain. Index contours are labeled, and the contour interval can be determined by counting the number of intermediate contours displayed between the indexes.
"So if you see an index contour that's labeled at 8,000-feet and you are located near that index contour, you know you're approximately 8,000 feet," explains Fishburn. "The index contour's labeled every 100-feet, and the contour interval is 20-feet. So my intermediate contours would be 8,000, 8,020-feet, 8,040-feet, 60-feet, 80-feet, and then 8,100-feet."
The lines on a topo map are colored, and can be curved, straight, solid or dashed.
Find more detail about reading a topographic map at howstuffworks.com
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