GEOL& 101

Topographic Map Lab

Created originally by Tom Braziunas and Gwyneth Jones, modified since then with permission.

I. Brief Background on Topographic Maps

A topographic map is a precise, graphic representation of the three-dimensional shape of the earth's surface. Topographic maps are used by surveyors, engineers, and geologists, as well as hikers, back packers, and other outdoor recreationalists. A standard topographic map uses contour lines to express elevations above sea level and show the shape of the land. A topographic map may or may not include shaded relief to help visualize steep slopes.

Topographic maps use horizontal controls to give location, scale and directions on a map. A geographic grid system of latitude and longitude (in degrees) is accurately established by field surveys. 

Latitude and longitude are not the only horizontal location system shown on topographic maps. Many topographic maps also show the universal transverse Mercator (UTM) grid, which is commonly used by GPS equipment.

In the United States, the Township and Range grid is used on standard topographic maps produced by the US Geological Survey. It breaks the country down into numbered sections of about one square mile each. If you are a property owner in the United States, the deed for your property describes the property boundaries in terms of the Township and Range system.

The latitude and longitude system specifies locations on the earth's surface in terms of degrees north or south (latitude) and east or west (longitude). Each degree is divided into sixty minutes (1 = 60'), and each minute is divided into sixty seconds (1' = 60").

The letters N and S are used with latitude to specify north and south. For example, a latitude of 48 degrees, 15 minutes, 28 seconds in the Northern Hemisphere would be written 48 15' 28" N. For longitude, the capital letters E and W are used for east and west, such as 11035' 51" W. Sometimes, in order to enter pure numbers into a database, latitude and longitude are expressed as positive numbers for N and E and negative numbers for S and W.

Two types of scales are shown on US Geological Survey topographic maps: (1) a precise representational fractional scale expressed as a ratio, for example, 1:24,000 means one inch on the map represents 24,000 inches in reality; and (2) a linear (bar) scale is an approximate practical scale that helps one measure distances (for example, a bar showing that 1 inch equals approximately 2 miles).

Vertical control uses contour lines to show correct elevation and the shape of the terrain. A contour line connects all points of equal elevation. It is determined by fixing certain elevations in the field and measuring up or down from these points. These control points are established permanently by using a metal marker set in concrete with the elevation engraved in it -- called a bench mark (BM). Contour lines always run at right angles to the direction of the slope and, as stated, all points along each contour line are at the same elevation.

This exercise begins your introduction to the "vertical control" of contour lines in, we hope, an entertaining way by using scanned parts of real topographic maps. You will gain more experience with the "horizontal control" of latitudes and longitudes and distances from the second part of the lab exercise, when you use a real, printed topographic map.     

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II. Virtual Lessons

Portion of a topographic map of Egypt from 1932 showing Egyptian script and buildings of the Great Pyramid complex. The Great Pyramid itself, which was built several thousand years ago, is the largest pyramid shown on the map. You can tell that this is part of a topographic map because of the brown contour lines, which, like the edges of terraces, follow the horizonal lay of the land.

Here are a few external web sites with interesting and educational information on topographic maps (such as the Egyptian topographic map above; image from the US Library of Congress).

PLEASE CAREFULLY READ THE INFORMATION ON TOPOGRAPHIC MAPS FROM THE INFORMATIVE WEBSITE BY MARK MCNAUGHT AT MOUNT UNION COLLEGE IN ALLIANCE, OHIO: Mark's Topographic Map Tutorial

THE UNITED STATES GEOLOGICAL SURVEY WEBSITE ALSO HAS A CHART SHOWING THE COMMON SYMBOLS ON TOPOGRAPHIC MAPS: http://topomaps.usgs.gov/ .

In addition, here are a couple other interesting websites to check out:

 

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III. Online Map Exercises

 You can click on the images to view them in a separate browser window.

CARKEEK PARK QUESTIONS #1 - 4:

Topographic map showing part of a creek in Carkeek Park, Seattle. 

To the left is a small portion of a topographic map showing a road and a creek (blue-green line) in Carkeek Park in Seattle.  North is always toward the top of topographic maps such as this.

Q.1: Using the "Rule of V's" determine which way is the creek flowing.
     a.  north-to-south
     b.  south-to-north
     c.  east-to-west
     d.  west-to-east

Hint: You will find the section on "Streams and Stream Valleys" in Mark's Map Tutorial to be especially helpful for deciding which way the creek is flowing.

Q.2: What do the little black boxes denote?
     a.  bench mark
     b.  small park, reservation, or monument
     c.  quarry or open pit mine
     d.  building

Hint: There is a guide to "Topographic map symbols" on the USGS website mentioned above. These squares don't represent gas wells but instead are the same as the rectangles in the guide.

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More of Carkeek Park is displayed on the portion of topographic map shown below. Note that every fourth contour line is heavier and labeled with heights in feet (these heavier lines are "index contours"). The spacing between adjacent contour lines (all contour lines including the lighter ones) is called the "contour interval".

Portion of topographic map that shows stream in Carkeek Park, Seattle, crossing several contour lines.

Q.3: What is the contour interval of this map?
     a.  10 feet
     b.  25 feet
     c.  50 feet
     d.  100 feet

     
Hint: Carefully count the number of contour lines between index contours.
Q.4: What is the elevation difference between the two red arrows?
     a.  10 feet
     b.  25 feet
     c.  50 feet
     d.  100 feet 
 
  • GREEN LAKE QUESTIONS #5 - 6:

    Portion of topographic map showing Green Lake and part of its surroundings.

    The contour interval on this map is 25 feet.

    Q.5: What is the approximate elevation of Green Lake?
         a.  75-100 feet
         b.  100-125 feet
         c.  125-150 feet
         d. 150-175 feet 
    Hint: Find the closest contour line and determine its elevation. The lake level must be BELOW that contour line's elevation but ABOVE the next lower contour elevation.
     
    Q.6: Which corner of the map shows the highest elevation?
         a.  northeast
         b.  northwest
         c.  southeast
         d.  southwest
    Hint: Look for the index contour line closest to the corner and then determine the elevation of thee contour line in the very corner. The corner itself must be ABOVE that contour line's elevation but BELOW the next higher contour elevation.
     

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    BLAKE ISLAND QUESTION #7:

    The next map shows Blake Island in Puget Sound. By now, you have learned how to read that the highest point on Blake Island is between 250 and 275 feet. The contour interval of the map is 25 feet and the index contours are every 100 feet. The numbers "25" and "36" are related to the Public Land Survey System. The next two maps will illustrate some additional interpretations of contour lines.

    Portion of a topographic map showing Blake Island in Puget Sound, west of Seattle.

    Q.7: From which direction would it be easiest to climb from the shore to the top of Blake Island?
        a.  From the Northwest
         b.  From the Southwest
         c.  From the Southeast 
         d.  From the Northeast
     

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    GRAND CANYON QUESTIONS #8 - 9:

    This topographic map shows the Isis Temple, a high-elevation (7012 foot) butte in the Grand Canyon. You will notice that the contour lines are closer at some elevations (the steep cliffs) and more broadly spaced at other elevations (the gentler slopes).

    Portion of a topographic map showing Isis Temple in the Grand Canyon, Arizona.

    Q.8: What is the contour interval, and how far apart are "index contours"?
         a.  contour interval-5 feet, index contours-25 feet
         b.  contour interval-10 feet, index contours-50 feet
         c.  contour interval-25 feet, index contours- 125 feet
         d.  contour interval-80 feet, index contours-400 feet

         
    Hint: Remember that the contour interval is the elevation difference between contour lines.
                 The "index contours" are the darker, labeled ones.

    Q.9: Approaching from the south, the steepest cliff occurs between which adjacent INDEX contours?
         a.  4800 and 5200 feet
         b.  4400 and 4800 feet
         c.  4000 and 4400 feet
         d.  3600 and 4000 feet 

     

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    FLORIDA QUESTION #10:

    This map shows a sinkhole region in Florida. Note that hachure marks mean that the contour lines drop in elevation instead of rise. Some of these sinkholes are deep enough to be filled with water to become lakes.

    Portion of a topographic map of part of Florida.

     

    Q.10: What is the contour interval, and how far apart are the "index contours"?
         a.  contour interval-5 feet, index contours-25 feet
         b.  contour interval-10 feet, index contours-50 feet
         c.  contour interval-25 feet, index contours- 125 feet
         d.  contour interval-80 feet, index contours-400 feet


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    REMAINING QUESTIONS BASED ON AN ACTUAL, PRINTED TOPOGRAPHIC MAP:

    Your instructor will have loaned you a topographic map, in which case DO NOT write or draw on the map, and do not fold it.

    Alternatively, you may have been given instructions on how you are to acquire a specific topographic map for yourself, and you will have acquired it as instructed.

    Q.11: What is the name of the quadrangle map that you are working with?

    Q.12: What size quadrangle is the topographic map?
         a. 60 minute
         b. 30 minute
         c. 15 minute
         d. 7.5 minute

    Q.13: What fraction of a degree of latitude does the map quadrangle span? (Hint: Divide your answer to the previous question by the number of arc minutes in a degree.)
         a. one whole degree of latitude
         b. one half of a degree of latitude
         c. one fourth of a degree of latitude
         d. one eighth of a degree of latitude

    Q.14: What fraction of a degree of longitude does the map quadrangle span?
         a. one whole degree of longitude
         b. one half of a degree of longitude
         c. one fourth of a degree of longitude
         d. one eighth of a degree of longitude

    Q.15: What is the latitude of the northern boundary of the map? (Remember that when writing latitudes, you must write N after the degrees, minutes and seconds if it is in the Northern Hemisphere, or S if it is in the Southern Hemisphere.)

    Q.16: What is the latitude of the northern boundary of the map?

     

    Q.17:  What longitude is the eastern boundary of the Mt. Adams map? (When writing longitudes, you must write E after the degrees, minutes and seconds if it is in the Eastern Hemisphere, W if it is in the Western Hemisphere.)
     

    Q.18:  Based on your answers above, which is a true statement?
         a.  The quadrangle is in the northern hemisphere and the western hemisphere.
         b.  The quadrangle is in the northern hemisphere and the eastern hemisphere.
         c.  The quadrangle is in the southern hemisphere and the western hemisphere.
         d.  The quadrangle is in the southern hemisphere and the eastern hemisphere.
         e.  None of the above can be determined with just this map.

    Q.19:  What is the fractional scale on the map? (It is expressed as 1:XXXX, where your answer is the correct number for XXXX. You can think of it as 1 inch on the map represents XXXX inches in the real world.)
     

    Q.20:  Based on your answer to question 17, one inch on the map represents how many miles in the real world? As always when asked to calculate, show your calculations!

    (Hint: Divide the XXXX number from the previous answer into the number of inches in a mile. The number of inches in a mile is 12 times the number of feet in a mile.)

     

     

    Q.21:  What was the magnetic declination of the map at the time it was published?

    (Remember to state not only the number of degrees but whether magnetic north was east of true north or west of true north.)
      

    Q.22:  If you were interested in the land just to the southeast of the map, which topographic quadrangle map would you get?

    Q.23:  What is the contour interval for the map?

    Q.24:  What is the index contour interval (the contour interval between index contours) on the map?

     

    Q.25:   What is the highest elevation labeled for a peak or hilltop on the map?

    Q.26:  What is the latitude of that highest altitude labeled point on the map?

    State the answer in degrees, minutes, and seconds as precisely as you can determine it.

    Q.27:  What is the lowest elevation on the map?

    Hint: It may be lower than lowest labeled elevation, in which case you should write "The lowest elevation on the map is lower than _____ (the last contour line before that point on the map) and higher than _____ (the elevation of what would be the next contour line down in elevation, which is not seen on the map.

    Q.28 (a): Does your map have sections labeled in red numerals, such as section 5 or section 28?
            (b) If it does, what is the approximate distance across each section?

         

    Q. 29: How many sections are there in each township and range?

    Hint: A township is six sections across, and so is a range. Multiply.


    Q.30 (a):  What is the definition of a contour line?

     

     

    Q. 30 (b): What color are the contours on your topographic map?