Use Them

A map, for the purpose of an amateur collector, is a generalized representation on a flat surface of some aspect of the surface of the earth. It may be a road map, such as those that filling stations give away; a topographic map, which expresses a third dimension through such a device as contour lines; or a geologic map or other more specialized type that shows the nature of the surface rocks, or economic and geographical features.

ROAD MAPS

In this automobile age, the collector will, of course, find road maps invaluable. They direct him to where he hopes to collect by the shortest, fastest or most convenient route. A few even indicate paleontological sites such as petrified forests, and fossil fish beds.

But the serious collector will wish to have more precise and analytical information than he can get from a road map or atlas. It is not enough to be guided to a site; the collector needs to know more about the deposit in which he plans to collect. Much of this information he can learn from maps before he ever takes to the road, and there is always more to learn when he gets to his destination. It is rarely possible to drive right to an undepleted fossil-collecting site, and locating the deposit itself usually calls for hiking guided by a good map.

TOPOGRAPHIC MAPS

The collector's best guide is the topographic map. Road maps do not show the steepness of hills, the depth of valleys, or even subtle changes of elevation in the prairie states. The topographic map adds the illusion of this third dimension by conventional symbols known as contour lines. These show the relief of the landscape, which is the difference of elevation of hills, valleys, and other natural features. Thus they show height, which is the difference of elevation of two nearby objects, and elevation, which is the height figured from a base plane, usually sea level, known as the datum plane.

In addition, these maps mark the position of man-made features, such as roads (including minor trails not shown on road maps), mines, quarries, and towns. In the topographic maps produced by the United States Geological Survey, water and ice, such as lakes and glaciers, are shown in blue; man-made objects and political boundaries are in black; major highways are in red; forested areas in green; and the contour lines are in brown. Other symbols are explained on the back of some of the maps, and a summary of the symbols is contained in the pamphlet "Topographic Maps," which may be had free from the Map Information Office of the Geological Survey, Washington, D.C. 20242.

Topographic maps are made to scale, that is, a distance on the earth's surface is portrayed by a proportionate distance on the map. The maps use several scales, but the most common are 1 inch to 62,500 inches, or roughly 1 inch to 1 mile; 1 inch to 24,000 inches; and 1 inch to 250,000 inches. The first is a medium scale useful for rural areas where a great deal of detail is not necessary; the second, a large-scale map for highly developed areas, shows individual buildings; and the last is useful primarily to cover an extensive area in one map.

The scale is shown in graphic form on the margin of the map. By marking off a distance on the map on a piece of paper, the user can compare the distance with the scale and get a reading of the distance in miles or feet. Maps are always made with the north direction at the top. Symbols on the margin indicate the true north and the magnetic north, which are usually several degrees apart, depending on location.

The United States Geological Survey has been mapping the United States and Puerto Rico since 1882. In Canada, similar maps are made by the Geological Survey of Canada, in Ottawa.

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