finding the difference in elevation between the two points from the contour lines (at each point you usually have to interpolating between adjacent contour lines),.using the map scale to find the real distance on the land surface,.measuring the distance between two points on the map,.

You can easily compute the local slope of the land surface, by: The best way to learn how to visualize topography from contour lines is to practice with a real map-and you will be doing that in the take-home exercise.įor a map at a given scale, the more closely spaced the contour lines, the steeper to slope of the surface: closely spaced contour lines mean steep slopes, and widely spaced contour lines mean gentle slopes (Figure 3-37). Or, even if you can’t do a good job of visualizing the topography, you at least have to understand how to interpret it from the contour lines. To be a sophisticated user of a topographic map, you have to be able to visualize the topography or 'lay of the land' by examining the contour lines. Interpreting Contour Lines on Topographic Maps A geologist often uses a topographic map as a base on which to plot geology in making a geologic map. Topographic maps are useful to both technical people (geologists environmental engineers) and to everyday people, like hikers. Viewing contours as the loci of horizontal planes with the land surface. Topographic contour lines.Īdjacent contours touch one another only where the land surface is vertical, and they cross one another only where one part of the land surface hangs over another part (and in such overhanging areas, by convention the contours are dashed or dotted to indicate the overhanging relationship, or just omitted altogether). The contours are formed by the intersection of these planes with the land surface. A good way to understand the concept of contours is to choose a series of elevations and imagine passing a corresponding series of horizontal planes through the landscape (Figure 3-36). A contour is a horizontal curve that’s the locus of all points on the map with the same elevation (Figure 3-35). Many maps of land areas have series of curved lines, called contours, that represent the topography of the area. The scale of map you work with depends on the level of detail you want to show on the map. Detailed geologic maps are often at scales of between 1:10,000 and 1:5,000. But often the detail of mapping that the geologist desires calls for a larger scale: that is, the map scale is such that a smaller land area is represented on a given sheet of paper. The resulting maps are called geologic quadrangle maps. The 1:25,000 maps are what geologists typically use as a base for mapping the geology of a local area.

These latter, newer, maps use the metric system for map distances and contour intervals. In addition, there is a series of maps with a scale of 1:250,000, called quarter-million maps. In recent times those quadrangle maps have been supplanted by seven-and-a-half-minute quadrangle maps that are about the same size at the old 1:24,000 maps but at a slightly different, but more rational scale of 1:25,000. Maps, called seven-and-a-half-minute quadrangle maps, that spanned 7-1/2' of longitude and 7-1/2' of latitude at a scale of 1:24,00.

Maps, called fifteen-minute quadrangle maps, that spanned 15' of longitude and 15' of latitude at a scale of 1:62,500, which is exactly one inch to the mile.

For many years there were two standard map scales:

Interpreting Contour Lines on Topographic MapsĪlmost all of the area of the United States has been represented on topographic maps at various scales.

Contour line topographic map