Experiment 1: Using a Topographical Map
Geologists study landforms and rely on topographic maps
(also called contour maps) published by the United States Geological Survey.
Topographic maps show the configuration of the Earth’s surface from an aerial
vantage point and illustrate the size and shape of three-dimensional land
surfaces by using contour lines that show elevation distance above sea level,
which has zero-foot elevation and vertical scale.
Contour lines do not intersect or separate; they always
rejoin to form a loop and have a set distance between each interval. Every few
lines, for instance, five lines, the index contour line will be marked bolder
than the rest to make map reading easier. The contour interval, the distance
between contour lines on the map, can be found using index contour lines. The
narrower, intermediate, and supplementary contours found between the index
contours help show more details of the land surface shape. If they are closer
together, the lines represent a steep slope and farther apart, a less steep
slope. To determine slope steepness, subtract the lowest elevation from the
highest. Divide that numerical result by the horizontal distance on the scale.
Stream gradient expressed in feet per mile can also be determined by measuring
a section of a stream, and then dividing its distance in miles into the
vertical difference in feet between the start and end sections.
USGS also uses other symbols, for example, a depression has
short lines perpendicular to the contour line known as hachures pointing toward
the depression. To denote a valley, contour lines often bend up to form a “v”
and a “u” for a stream crossing or gully. Vegetation, streets, buildings,
woods, trails, railroads, mines, craters, and other features also may be shown
in varying lines and colors. In this experiment, you will identify key features
on a topographic map using index contour lines, symbols, and indicated
landforms.
Materials
Topographic Map
Procedure
1. Study the
topographic map. Look for index contour lines, contour line spacing, symbols, and
indicated landforms. Then, answer the Post-Lab Questions,
Post-Lab Questions
1. What is
the contour interval of this map?
2. What is
the elevation on the peak of Poorman Hill? Poorman Hill can be found near the
western border of the map, midway between north and south.
3. Boulder
Creek is just south of Poorman Hill. Which is steeper, the banks of the creek,
or the area close to the peak of Poorman Hill? Explain how you determined this.
4. What is
the approximate elevation of Wonderland lake?
5. Mark any
peaks on the map with an X and list their elevations below.
ScholarMatic: Explanation & Answer
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