Name
GEOL.3250 Geology for Engineers
Topographic Maps and Profiles
A topographic map is a two-dimensional (flat) representation of a three-dimensional land surface. It shows
landforms such as hills, valleys, slopes, and coastlines, and their relief (difference in elevation) by using contour
lines to represent elevations. Contour lines are lines of equal elevation. In lab, you will learn how contour lines
represent land surfaces by following the rules listed below:
EXAMPLES OF HOW TOPOGRAPHIC MAPS DEPICT LAND SURFACES
Notice how the
rules for contour
lines are
followed.
Fill in elevations for the blank dots below and add contour lines with a 100-foot contour interval.
Construct a topographic map below by contouring these elevations.
Use a contour interval of 10 feet.
Complete the topographic map on the right. Use a contour interval of 100 feet. Start at sea-level, and pay
attention to contour rules for depressions.
Construct a topographic profile for this map from A to A’. Note the contour interval for your vertical scale
is in feet, but the horizontal scale (see scale bar below) is in miles. Use a piece of paper for your graph.
C.I. = 1000 feet
B
Slope:
The spacing of contour lines on a map indicates the slope of topographic features. Steep
slopes are shown by closely-spaced contour lines, while less steep slopes are indicated with
contour lines that are further apart. The average steepness between any two points can be
expressed either in terms of slope gradient or slope angle. The expression for calculating slope
gradient is:
slope gradient = rise = Δz
run Δx
Slope angle is simply the angle, the tangent of which is the slope gradient:
slope angle = arctan(slope gradient)
Answer the following questions using the map of Mauna Loa volcano, Hawaii:
1) Which slope is steeper, the one between Point A and Point B or the one between Point B and
Point A’? How can you tell?
2) What is the distance between Point A and Point B?
3) Calculate the slope gradient and slope angle between Point A and Point B.
4) Repeat steps 2 and 3 for the distance between Point A’ and Point B.
5) Do your calculations support your answer to question 1? Why or why not?
The following questions refer to the Black Mountain 7.5’ Quadrangle.
1. What is the scale of the map?
2. What is the contour interval?
3. What is the declination for the quadrangle in 1958?
4a. What is the bearing of a line from the peak of Hardluck Campground to Kinsey Ranch?
4b. What is the distance in feet between these two points?
In meters?
5a. What is the elevation in feet of the highest point on the Black Mt. Quadrangle?
5b. The lowest point?
5c. What is the total relief in the area covered by the map?
The following question references the Wingate Pass 15’ Quadrangle.
6. Use the graph paper provided to draw a topographic profile from Lone Willow Spring to
Brown Mountain. For the vertical scale, make 1 inch = 1000 ft (5.2 X vertical exaggeration).
Label the horizontal and vertical scales. Draw and label everything neatly. Include: title, your
name, general direction on the left and right sides of the profile (i.e. N, NW, SE), geographic
features (Panamint Valley, etc.).