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Follow the Lines

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Published on: Jun. 2, 1997

Last revision: Oct. 26, 2010

the map. For example, a 1:10,000 scale means that one inch on the map equals ten thousand inches of actual distance. In other words, one mile will take up a little more than six inches on the map.

A more common way of expressing scale is to say that so much distance on the map represents so much actual distance. For example,

1 inch might equal 10 miles or, on a more detailed map, 1 inch might represent 5 miles.

Likely the most universally used maps are those published by the United States Geographical Survey. These maps are available by mail through the USGS or at several authorized map dealers, often sporting goods stores or outdoor outfitters.

USGS maps range from a single map covering the entire state (1:500,000) to maps that take 2.64 inches to cover a single mile (1:24,000 or one inch equals 2,000 feet). You can contrast those numbers with the official State Highway Map of Missouri, on which 1 inch equals 13.5 miles or 855,360 inches.

The 1:24,000 USGS maps, also called 7 1/2 minute quadrangles, provide great and useful definition. They not only mark roads and railroad tracks, but also show buildings, cemeteries, landmarks, churches, creeks and springs.

Perhaps as important, the maps represent the topography or surface features of the land. At first glance, topographic maps look like the telephone desk pad of a doodler who's been three hours on hold. The placement of each one of those squiggly lines, however, imparts important information about the lay of the land.

The lines accurately depict hills, ridges, slopes, valleys and plains by representing exact levels of elevation. To understand how they do this, imagine a perfectly flat-bottomed cloud settling down to exactly 800 feet above sea level. Everything below that elevation would be clear and everything above foggy.

Lets say you ran a paint roller along the ground exactly where the fog line intersected the ground, including along the hillsides, perhaps circling a small peak and jogging in a bit where runoff has etched a gap into a slope. Imagine the cloud then raised 20 feet to 820 feet, and you drew another line. (For illustration purposes only; please don't attempt to do this at home.)

Later, after the sky has cleared, you get up in an airplane and take a picture of the area. Your paint lines on the two-dimensional photo would look exactly like those squiggly lines on a topographic map.

You can

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