Topographic Map Contour Lines
Contour lines are the greatest distinguishing feature of a topographic map . Contour lines are lines drawn on a map connecting points of equal elevation, meaning if you physically followed a contour line, elevation would remain constant. Contour lines show elevation and the shape of the terrain. They're useful because they illustrate the shape of the land surface -- its topography-- on the map. Here's a cool way to understand how to interpret contour lines: Take an object like a ball or a pile of laundry , and shine a red laser pointer along the object's side. The line you see will look like a contour line on a topographic map.
In order to keep things simple, topographic maps show lines for certain elevations only. These lines are evenly spaced apart. We call this spacing the contour interval. For example, if your map uses a 10-foot contour interval, you will see contour lines for every 10 feet (3 meters) of elevation -- lines at 0, 10, 20,
30, 40, and so on. Different maps use different intervals, depending on the topography. If, for example, the general terrain is quite elevated, the map might run at 80- to even 100-foot (24.4- to 30.5-meter) intervals.
This makes it easier to read the map -- too many contour lines would be difficult to work with. Look in the margin of your map to find out its contour interval.
To make topographic maps easier to read, every fifth contour line is an index contour. Because it's impractical to mark the elevation of every contour line on the map, the index contour lines are the only ones labeled. The index contours are a darker or wider brown line in comparison to the regular contour lines. You'll see the elevations marked on the index contour lines only. To determine elevations, pay attention to the amount of space in between lines. If the contours are close together, you're looking at a steep slope. If the contours have wide spaces in between -- or aren't there at all -- the terrain is relatively flat.
Problem: What techniques are necessary in order to successfully construct a contour map?
Vocabulary:
Contour line - Contour interval - Profile - Hachured contour lines -
Gradient - Change in Field Value -

Procedure A:
1.
Mark small horizontal lines on the side of the clear plastic box, if it hasn’t already been done. They should be one centimeter apart.
Measure from the inside; bottom to the top.
2.
Place the plastic volcano inside the box.
3.
Tape the plastic overlay to the top of the box lid.
4.
Begin filling the box with colored water, stopping when the water level reaches the first mark. This is sea level which is equal to 0 meters.
5.
Place the lid on the box and then, using an overhead marker, trace the
“shoreline” onto the plastic overlay.
6.
Taking off the lid, add more colored water until it reaches the next centimeter marking.
7.
Replace the lid and trace the new “shoreline”.
8.
Repeat this procedure for every marking until the volcano is completely under water. Include the “shoreline” of the lake as it forms in the crater.
9.
Create a contour map by tracing the contour lines from the plastic overlay onto a piece of plain white paper. It is helpful to lean against the exterior windows or do this on the overhead projector to help in tracing.
10.
Label each contour line starting with the first marking line. This is 0
meters in elevation. Label all the lines using a contour interval of 100 meters.
11.
The contour line at the top of the volcano should be drawn in as a hachured line, due to the depression.
12.
Attach your contour map to the lab write up. Each person needs their own map.

Procedure B:
1.
Orient your paper with the volcano on the left side as shown below. Draw a straight line lengthwise through the center of the volcano. Label the left end “A” and the right end “B”.
2.
Use a piece of graph paper to draw a profile of your contour map along line
A-B.
3.
Attach your profile to the lab write up. Each person needs their own profile.
4.
Using a scale of 1 cm=1 km, calculate the gradient on your map from Point A to the closet rim of the volcano and from Point B to the closest rim. Show all work in Tables #1 and 2.
A B
Table #1 Table #2

Table #1:
Elevation at Point A
Elevation of Rim of the Volcano
Difference in elevation from Rim to
Point A
Distance between Rim to Point A
Write the formula for Gradient
Substitute in the values
Record your answer with units
_______________________Meters
_______________________Meters
_______________________Meters
____________________Kilometers
Table #2:
Elevation at Point B
Elevation of Rim of the Volcano
Difference in elevation from Rim to
Point B
Distance between Rim to Point B
Write the formula for Gradient
Substitute in the values
Record your answer with units
_______________________Meters
_______________________Meters
_______________________Meters
____________________Kilometers

Questions:
1. What do contour lines represent?
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__________________________________________________________
2. Why is it unlikely that two contour lines will cross?
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__________________________________________________________
3. Referring to your map of the volcano, how does a contour map indicate areas of steep or gentle gradient?
__________________________________________________________
__________________________________________________________
4. Would a topographic map of a mountain constructed 10,000 years from now be identical to a map drawn in 2004? Explain your answer.
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__________________________________________________________

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