Topographic map a good outside tool

Steve Roark - Tri-State Outside

Courtesy of Steve Roark

Our area is geologically a bumpy place, with mountains, valleys, streams and other features. If you can read a topographic map you can keep up with where you are and find useful and interesting information.

A topographic map is similar to several kinds of maps, indicating the location of roads, buildings, caves, dams, ponds, streams and rivers. It is unique in that is also indicates the location of ridges and valleys and gives the elevation of any point on the map. This is done using a series of lines called contour intervals, each indicating a different elevation level. Most topo maps have contour intervals of 20 feet, meaning each line is 20 feet higher or lower than its neighbor. Contour lines running close together indicate steep hills, while those wide apart indicate more level land.

The trick to reading topo maps is learning to identify geographic features by the shape of the contour lines. Ridges appear as a series of lines running close together, with occasional circular shapes in the middle. These circles represent ridge peaks, and are fairly easy to discern. U shaped contour lines indicate side (I call them spur) ridges coming off a main ridge. V shaped lines indicates drains between ridges. Another hint is that if the mouth of the U or V faces the ridge, it’s a spur ridge. If the mouth of the U or V faces away from the main ridge, it’s a drain (or hollow as we locals call them). A blue line in a drain indicates a running stream. Topo maps use green to indicate forested areas, and white to indicate cleared land.

For land management decisions, topo maps are priceless. Since they indicate the steepness of land, they help farmers determine land use for cropland or forestland. Determining the direction land faces (called aspect) gives you an indication of soil moisture. East and north slopes tend to be moist, south and west slopes are dryer. Soil on lower slopes tends to be deeper, becoming shallower on upper slopes and ridge tops. This information is very useful to foresters in determining which tree species to manage for. Topo maps are to scale, and so are useful in determining land acreage and distances. Standard topo maps have a scale of one to 24,000; meaning 1 inch on the map represents 24,000 inches in the field. In feet one map inch equals 2000 feet.

Topographic maps are developed by the U.S. Geographic Service (USGS), and are available at map stores. Each map covers a certain land area called a quadrant, which has an identifying name, such as Middlesboro South. You can order or download topo maps online at the USGS Map Store. You can also call them at 888-275-8747. Some other online topo map sites is TopoZone and Gmap4, so do a search and check them out.

Steve Roark is the area forester in Tazewell, Tennessee, for the Tennessee Department of Agriculture, Forestry Division.

Courtesy of Steve Roark of Steve Roark

Steve Roark

Tri-State Outside

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