![]() Topographic maps have contour lines that connect points of identical elevation above sea level.Topographic maps are 2-dimensional representations of the 3-dimensional surface features of an area.On a large scale geologic map, colors represent geological provinces. Bathymetric maps help oceanographers visualize the landforms at the bottoms of lakes, bays, and the ocean as if the water were removed. Numbers are low near sea level and become higher with depth. The bathymetric map in the Figure below is like a topographic map with the contour lines representing depth below sea level, rather than height above. Common scales used in United States Geological Service (USGS) maps include the following:Īn animation showing contour lines and the slopes they represent. The horizontal scale can be used to calculate the slope of the land (vertical height/horizontal distance). Scales on topographic maps indicate horizontal distance. Where the water flow is light or nonexistent, there is no longer a blue line, but the contour lines point uphill indicating that the stream channel is still there (see the map of Stowe in Figure above).ĥ. Coming out of the T on the other side, you can follow the blue stream uphill (southeast). A blue stream goes downhill (northwest) into a lake. In the map of Stowe, where does a stream run downhill into a lake? If the stream contains water, the line will be blue otherwise, the V patterns indicate the direction water will flow. The channel of the stream passes through the point of the V and the open end of the V represents the downstream portion. Where a stream crosses the land, the Vs in the contour lines point uphill. V-shaped expanses of contour lines indicate stream valleys. On a contour map, a circle with inward hatches indicates a depression.Ĥ. The map legend gives the contour interval. This difference between contour lines is called the contour interval. Two contour lines next to one another are separated by a constant difference in elevation (such as 20 ft or 100 ft).After all, a single point can only have one elevation. The contour lines run next to each other and NEVER cross.Every fifth contour line is bolded and labeled with numerical elevations. Each contour line represents a specific elevation and connects all the points that are at the same elevation.For example, the road bends in order to go around a hill or stops at the top of a mountain. While a road map shows where a road goes, a topographic map shows why. Contour Lines and IntervalsĬontour lines connect all the points on a map that have the same elevation and therefore reveal the location of hills, mountains, and valleys. Mathematically, a contour line is a curve in two dimensions on which the value of a function f(x, y) is a constant. If you walk along a contour line you will not go uphill or downhill. A contour line is a type of isoline in this case, a line of equal elevation. Topographic maps use contour lines to show different elevations on a map. Topographic maps represent the locations of geographical features, such as hills and valleys. Mapping is a crucial part of Earth science. Rock units and geologic structures are shown on geologic maps. ![]() Maps are extremely useful to Earth scientists to represent geographic features found above and below sea level and to show the geology of a region.
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