Geography 101 Lab 16
Introduction to Topographic Maps – Practice Questions
You should be able to draw contour lines from spot elevations.
1.
Draw contour lines at a twenty-foot interval from the spot elevations in Figure 1 starting with a low of 1080 feet. The
blue lines are rivers.
Figure 1
You should be able to use a representative fraction to calculate distances separating points on a map.
Conversion factors: 12 inches = 1 foot
5280 feet = 1 mile
2.
The distance from point A to point B on the Hamburg, WI map in Figure 2 is 3.7 inches. How many miles separate these
two points on the earth’s surface?
Method 1: 24,000
1
1
3.7 24,000 88,800
3.7
1.4
1
12
5280
12 5280
63,360
1
Method 2: Rewrite map scale so the units on the right side of the scale are miles, not inches. 1 map in = 24,000 earth inches; convert earth inches to feet: 24,000/12 = 2000 1 map in = 2000 ft; convert feet to miles: 2000/5280 = 0.38 1 map in = 0.28 miles 0.38
3.7
1.4
1
1
Method 3: do the math one step at a time. 1. Calculate earth inches by multiplying 3.7 times the map scale: 3.7 map inches × 24,000 = 88,800 earth inches 2. Convert inches to feet: 88,800/12 = 7400 feet 3. Convert feet to miles: 7400/5280 = 1.4 mi 3.
The distance from point A to point B on the Palmerton, PA map in Figure 3 is 3.9 inches. How many miles separate
these two points on the earth’s surface?
24,000
1
1
3.9 24,000 93,600
3.9
1.5
1
12
5280
12 5280
63,360
1
4.
The distance across the bottom of the Lehigh River valley on the Palmerton, PA map in Figure 3 is 0.25 inches. How
many feet is it across the valley bottom on the earth’s surface?
24,000
1
0.25 24,000 6000
0.25
500
1
12
12
12
1
The distance separating points A and B on the Allentown, PA-NJ map in Figure 4 is 1 inch. How many miles separate
these two points on the earth’s surface?
Note: it makes no difference that the elevations on the Allentown map are in meters. The representative fraction can be used with any unit of measurement. Method 1: 100,000
1
1
1 100,000 100,000
1
1.6
1
12
5280
12 5280
63,360
1
Method 2: Rewrite map scale so the units on the right side of the scale are miles, not inches. 1 map in = 100,000 earth inches; convert earth inches to feet: 100,000/12 = 8333.3 1 map in = 8333.3 ft; convert feet to miles: 8333.3/5280 = 1.58 1 map in = 1.6 miles 1.6
1
1.6
1
1
Method 3: do the math one step at a time. 1. Calculate earth inches by multiplying 1 times the map scale: 1 map inches × 100,000 = 100,000 earth inches 2. Convert inches to feet: 100,000/12 = 8333.3 feet 3. Convert feet to miles: 8333.3/5280 = 1.6 mi 5.
You should be able to calculate elevation gradients from topographic maps.
6.
7.
Points x and y on the Hamburg, WI map in Figure 2 are 0.5 inches apart. What is the gradient between these two
points in feet/mile?
1. Calculate the change in elevation between points x and y: 1340 ft – 1250 ft = 90 ft 2. Calculate the distance separating points x and y in miles. 24,000
1
1
0.5 24,000 12,000
0.5
0.2
1
12
5280
12 5280
63,360
1
3. Calculate the gradient: 90
∆
450 / 0.2
Points x and y on the Palmerton, PA map in Figure 3 are 0.8 inches apart. What is the gradient between these two
points in feet/mile?
1. Calculate the change in elevation between points x and y: 1200 ft – 400 ft = 800 ft 2. Calculate the distance separating points x and y in miles. 24,000
1
1
0.8 24,000 19,200
0.8
0.3
1
12
5280
12 5280
63,360
1
3. Calculate the gradient: 800
∆
2667 / 0.3
You should be able to interpret contour lines correctly, including determining their elevation using the contour
interval, assessing gradient based on contour line spacing, and identifying hills, valleys, and other landforms
based on contour line patterns.
8.
Compare the contour line spacing at the two locations for which you calculated gradients in questions 6 and 7.
The contour lines are much closer together on the Palmerton map and the Palmerton map has a much steeper gradient. The closer the contour lines the steeper the gradient. 9.
If there were no elevation labels associated with the contour lines on the Hamburg, WI map in Figure 2, could you still
determine that points A and C sit on hilltops? Explain.
Yes. The contour lines surrounding the letters are closed. Closed contour lines indicate high spots. 10. How does the gradient on the ridge between points C and D on the Palmerton, PA map in Figure 3 change on the ridge
top compared to the sides of the ridge? Explain.
The gradient on the sides is quite steep while the top of the ridge is relatively flat. The contour lines are very close together on the sides of the ridge, but at the top, the contour lines are farther apart. 11. Based on the shape of the contour lines on the Hamburg, WI map in Figure 2, in what direction is Einert Creek flowing?
Explain.
Einert Creek is flowing from east/northeast to west/southwest. The 1250 ft contour line forms a V when it crosses Einert Creek and the V points to the east/northeast. The V points upstream. 12. Although no stream appears at the location of the line marked m–n on the Hamburg, WI map in Figure 2, a stream could
be located here. How can you tell this is a possible location for a stream?
The contour lines that cross line m–n bend uphill (form V’s pointing uphill), which is what contour lines do when they cross rivers. 13. What’s the best estimate of the elevation of point z on the Hamburg, WI map in Figure 2?
1245 feet. The contour interval = 10 feet. Since z is in between the 1250 index contour and the 1240 intermediate contour, add half the contour interval to 1240. 14. If you walked along the line labeled s–t on the Hamburg, WI map in Figure 2, what type of landform would you be
walking across?
You would be walking up over a ridge and down the other side. The contour elevations increase and then decrease. 15. Line C–D on the Allentown, PA-NJ map in Figure 4 crosses a ridge (as does line A–B). If the word “Ridge” didn’t
appear on the Allentown map, could you still determine that a ridge exists here? Explain.
Yes. There is a string of closed contour lines and closed contour lines indicate high spots. 16. A series of ridges exist on the Allentown PA-NJ map in Figure 4 that run approximately parallel to each other and stretch
the length of the map. Draw a line along the top of each of these ridges. How many ridges appear on this map?
17. The maps in Figures 2 and 3 have the same scale but their contour intervals are different. Why?
The total relief on the two maps is very different. The total relief of the Hamburg, WI is approximately 1375 (elevation of point A) – 1235 (elevation of Big Rib River where it flows off the south edge of the map) = 140 feet. The total relief of the Palmerton, PA map is approximately 1440 feet (intermediate contour left of point A) – 380 (elevation of intermediate contour line adjacent to Lehigh River) = 1060 feet. If the Palmerton map had a 10‐foot contour interval, you wouldn’t be able to distinguish the lines from one another. Plus, the lines would obscure other information on the map. If the Hamburg map had a 20‐foot contour interval, you wouldn’t be able to see any details regarding the relief. You should be able to draw a topographic profile with a given vertical exaggeration.
18. Draw a profile of the topography along lines A–B and A–C on the topographic map of Hamburg, WI shown in Figure 1.
Use all the contour lines (index and intermediate) to draw these profiles. Draw the profiles with a 20X vertical
exaggeration. Add all the necessary labeling to the profile so a reader can understand exactly what you did. You can
draw the profiles side-by-side with a little bit overlap between the right side of the A–B profile and the left side of the
A–C profile.
See profile below map. 19. Draw a profile of the topography along lines A–B and C–D on the topographic map of Palmerton, PA shown in Figure
2. Use just the index contour lines to draw these profiles. Draw the profiles with a 10X vertical exaggeration. Add all
the necessary labeling to the profile so a reader can understand exactly what you did. You can draw the two profiles
with a little bit of overlap between the right edge of one profile and the left edge of the second profile.
See profile below map. 20. What is the approximate local relief for the Big Rib River valley according to the profile you drew from the Hamburg,
WI map? What is the approximate local relief for the Lehigh River valley according to the profile you drew from the
Palmerton, PA map?
Big Rib River: approximately 100 feet. Lehigh River: approximately 1000 feet 21. If you want to compare the river valley in Wisconsin to the one in Pennsylvania, is it OK to use the two profiles you
drew for questions 17 and 18? Explain.
No, it is not OK because the profiles do not have the same vertical exaggeration. Only compare profiles with the same vertical exaggeration. If you didn’t look at the elevations on the y‐axis, you might think the Lehigh River valley was only slightly deeper than the Big Rib River valley when in fact it is 10‐times deeper. You should be able to describe the color coding used for categorizing topographic map symbols.
22. What do the following colors generally represent on topographic maps?
Areas shaded green – forested areas
Areas shaded red – urban areas
Brown lines – contour lines
Thick brown lines – index contours; have elevation labels
Thin brown lines – intermediate contours; follow contour interval
Dotted brown lines – supplemental contours; drawn at half the contour interval
Areas shaded blue – water bodies (e.g. lakes)
Solid blue lines – perennial rivers (flow all‐year round)
Blue lines drawn as a dash and three dots – intermittent streams (flow only part of the year)
Red lines – survey lines or roads
Black lines – political boundaries or roads
Features drawn in purple – updated information
You should be able to differentiate small-scale maps from large-scale maps and describe how the scale of a
map affects the representation of the landscape.
23. Compare and contrast the characteristics of the Palmerton, PA map (Figure 3) and the Allentown, PA-NJ map (Figure 4)
with regard to the following:
Palmerton, PA
Allentown, PA-NJ
Representative Fraction
1:24,000 1:100,000
Amount of detail shown
Lots of details; road names shown Little detail; no road names; small roads not shown
Amount of land area covered
Small area Large area
Contour interval in feet
20 feet 20 m: 20 × 3.281 = 65.62 feet
Total relief in feet
≈1060 feet 500m (lookout) – 120m (Lehigh River valley) = 380m; 380 × 3.281 = 1247 feet
Size of ridge Lehigh
River cuts through
Large; ridge occupies
most of map
Small; just one of several ridges shown on map
Length of line (inches)
C-D about 3.7 inches
A-B about 1 inch
24. Based on your answers to question 22, which map has a smaller scale?
The Allentown map has a smaller scale. 25. Line A–B on the Allentown, PA-NJ map (Figure 4) crosses the same ridge as line C–D on the Palmerton, PA map
(Figure 3). Why is line A–B on the Allentown map shorter than line C–D on the Palmerton map?
Because the Allentown map has a smaller scale. Features are smaller on small scale maps than on larger scale maps. 26. Why does the Palmerton map (Figure 3) have a larger contour interval than the Allentown map (Figure 4)?
The difference in local relief is not sufficient to warrant a change in the contour interval. The key reason is the change in the map scale. Since the Allentown map covers a much larger area, there isn’t enough space to draw contour lines at a 20‐foot interval. Figure 2
y
x
s
t
z
n
m
Figure 3
x
y
Figure 4