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Regional Geology |
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Introduction/Contour Maps |  |
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It can be said that maps are to the Earth scientist as money is to a banker. Maps provide a medium to document the smallest features of a crystal lattice or the grand landscape of an entire ocean basin. This unit addresses notions of mapping certain dimensions of the Earth's space and time. |
By Lindsay Craig
Objective: At the end of this lesson you will be able to read and model contour topographic maps.
Reason: Topographic maps are highly useful and have a broad range of potential applications.
Activity #1. In a complete paragraph answer the following questions:
What different ways have you used maps? Where were you and what were you doing? Think of other people who used maps, why did they use them?
The adjacent
image is of a standard 1:24000-scale United States Geological Survey (USGS)
topographic contour map (paper copy) of the Virginia City Quadrangle, Nevada.
Note the altimeter, the compass and the quarter (upper right corner)
for scale. On these maps topography is displayed through use of contours.
Contours are lines of equal elevation. You will soon have the opportunity
to examine this map in closer detail.
These are three of the main reasons to learn how to use topographic contour maps:
If you were trying to get to the Comstock Lode 140 years ago to stake your
claim and get rich, your way would have been difficult and dangerous. You
would have had to cross a vast wilderness on foot or by horse. A simple
sketching for a map would be the best you would have to help you along the
way. There were no highways and no cars. Imagine having to travel across
the country without a real map and having to walk or ride a horse the entire
way. As the wilderness became explored and settled, maps became increasingly
detailed. There was a strong need to have the land mapped and surveyed.
Topographic or contour mapping was developed to represent the three dimensional
(3D) character of the landscape on paper, which is a 2D medium. These maps
became an instant success because they could be used by anyone, including
the traveler, engineer and geologist alike. Modern public domain topographic
maps are available for every portion of the United States. These
uncopyrighted maps are produced by the United States Geological Survey and
are available at several different scales at affordable
prices.
A small portion of the USGS Virginia City topographic map is shown; it includes Mt. Davidson (7864 feet above sea level) and Mt. Bullion (7682 feet above sea level). The contour interval is 40 feet, or in other words the elevation change between each line is 40 feet. Notice that there are bold lines at even 200-foot contours, such as the 7000-foot contour interval. Also notice that along ridgelines the contours make a "V " pattern that points outwards from the ridge. In ravines the contours point into the ravine. The patterns look the same but the "V" along the ridges point horizontally into the air while those in the creek point horizontally into the ground.
Compare the ridgeline that leads from the northwest towards Mt. Davidson; in your own words how is it different from Bullion ravine and yet how does it look the same (think about what was stated above)?
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Introduction/Contour Maps | |
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