Read through Appendix C in your text for additional background.
You should review a brief power point presentation about topographic maps
A Topographic map shows the variations in elevation of the area represented on the map with contour lines. A contour line on a map connects points that are at the same distance above, or below, sea level (or some other reference surface). For example, the 20' contour line connects all points on the map that are exactly 20' above sea level.
For each map a contour interval is selected; this is the vertical distance between adjacent contour lines. If the contour interval is 10', then the next highest contour line is the 30' line and the next lowest is the 10' line. If a point on a map is between the 20' and the 30' contours all you know is that the point is greater than 20' above sea level and less than 30' above sea level; you can not "guess" the exact elevation.
The spacing of contour lines on a map tells you how "steep" the slope is. Take a bowl and turn it upside down on a table. The top of the bowl lies furthest from the table. The contour lines would be circular and equally spaced. This map of a dome shows steep sides to the north but more gentle slopes to the south. The closer together the contour lines are, the steeper the slope.
Question - Contour lines can't cross. Why? However, contour lines could lie on top of each other. When might that happen?
Thus, a topographic map allows your to "see" the features present on the surface that are being represented.
Print a copy of this map. The numbers given are the elevations of specific locations in feet above sea level. The contour interval is 20'. Start with the 80 foot contour line. All points between 60 and 80 feet will lie between the 60 and 80 foot lines. The lowest point on your map is 67 feet so you don't need to draw in the 60 foot contour line. Note that most of the points will not lie on a contour line but will lie between adjacent contour lines. Start up near the top left side of the map. The 80 foot line will go between the points labeled 78x and 82x. Continuethe line so that it goes between the points labeled 71x and 83x. Make your line as smooth as possible. When you are satisfied with the 80 foot contour line draw in the 100 foot contour line. All points between 80 and 100 feet in elevation will lie between the 80 and 100 foot contour lines. If a contour line crosses a stream it will "V" upstream as noted in the references above. Make sure that you label the contour lines on your map.
You don't need to do the following but think about it. Suppose you wanted to change the contour interval (CI) to 10 feet. Can you visualize where these extra lines would go and how they would appear?
Complete the map and hand it in on the due date. The faculty at Cavin College have constructed a nice introduction to Topographic Maps. Spend some time reviewing the properties of these maps. Then, take the Quiz. There is nothing to hand from the Calvin College quiz in but write me a brief paragraph in which you tell me if you find it easier to learn interactively (with aids like the Calvin College example) or if you prefer a text book approach.
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Copyright by John C. Butler, July 29, 1995
