1. Introduction to Topographic Maps

2. Topographic Maps
Two dimensional model of the Earth’s surface (represents 3-D world)
Topographic maps are also known as contour maps.
Show elevation above sea level using contour lines.

6. “Real World”
Contour Map

7. Topographic Maps Contour Line –
- line on a map that connects points of EQUAL elevation.
- show elevation and shape of the land
Relief – Difference between high and low elevations

9. Topographic Maps Contour Interval –
difference in elevation between each line. MUST be equal spacing.
Contour interval =
20 feet
580
560
540
520

10. Topographic Maps Index Contour –
Usually every 5th line is printed darker and has an elevation printed on it.

12. Rules for Contours
Contour lines never cross

13. Rules for Contours
2. Contours form closed loops (even if not shown of the map.

14. Rules for Contours
3. Contours bend upstream (uphill) when crossing a stream.

16. Tracking Flowing Water
How does water always flow?
DOWNHILL
How can we tell what direction (N,S,NW,ESE) is downhill?
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17. Tracking Flowing Water
You can look for elevation changes since water will flow from higher to lower elevations.
Here the stream flows toward the northwest.
2000 ft
2100 ft
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18. Tracking Flowing Water
You can look at the contour lines as they cross the stream. They will always point upstream.
Downstream
Upstream
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19. Rules for Contours
The maximum possible elevation for a hill is “1” less than what the next contour “should” be.
The highest possible elevation of the hill is just below the value of  the next line that is not shown 90 80 70 60 50

20. 399
179
239

21. Closely Spaced Contours
Steeper Slope (Gradient) – contour lines are closer together.

23. Wide Spaced Contours
Gradual/Gentle Slope (Gradient) – contour lines are farther apart.

25. A B

26. Steep or flat? We need to calculate a terrain gradient.
You can tell whether a region on a map is steep terrain (hill/mountain) or relatively flat (plain) by looking at contour lines.
HOW?
We need to calculate a terrain gradient.
This is the change in elevation over the
change in distance along the ground.
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27. Steep or flat? Elevation change Elevation change 0.5 mile distance
= 20 feet
Gradient 20ft/0.5 mi = 40 ft/mi
Flat
Elevation change
= 600 feet
Gradient 600ft/0.5 mi = 1200 ft/mi
Steep
0.5 mile distance
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28. Contours and Profiles
You can generate a profile of a landform from the contour lines on a topographic map.
Click on image
to see contours
develop
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Simple contour map

29. Depressions
Contour lines which show a depression, crater, or sinkhole on a map.
Shown by dashed lines (hachure marks) on the inside of a contour line
The elevation of the first depression contour is the same as the lowest regular contour near it.

30. Rules for Contours
The lowest possible elevation for a depression is “1” more than what the next contour “should” be.
The lowest possible elevation of a depression is just above the value of  the next line that is not shown 90 90 51 80 70 60 50

31. 100
100 50

32. Benchmarks
a location whose exact elevation is known and is noted on a brass or aluminum plate.
bench marks are shown on maps by an X with the letters BM written next to them.

34. Map Scales
Indicates the distance on the map compared to distance in the real world
Graphical - by a line divided into equal parts and marked in units of length.

35. (There are 63,360 inches in a mile)
Map Scales
Numerically – usually by writing a fraction to show what part of the true distances map distances really are.
1:63,360
One inch on the map equals 63,360 Inches in the real world.
(There are 63,360 inches in a mile)

36. Gradient
A trail is four miles long as measured by the scale on a map. The beginning of the trail is at the 1,060 ft contour line and the end of the trail is at the 960 ft contour line. Calculate the gradient of the trail.
Gradient = =
1060 ft – 960 ft
4 miles
25.0 ft/mi

37. Contour Lines
Elevation is indicated by contour lines. A contour line is a line of equal elevations. All points on a contour line have the same elevation.
800 feet
700 feet
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38. Contour Lines
The elevation difference from one line to another is called the contour interval. On the map portion below the contour interval is 20 ft.
20 ft elevation decrease
20 ft elevation increase
20 ft elevation increase
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39. Contour Lines
The contour interval is usually printed on a topographic map.
However, you can always calculate the interval
from the lines with values.
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40. Review Questions How are contour lines drawn on maps?
How does a contour map show whether a slope is gentle or steep?
What is a benchmark?
How is a benchmark shown on a map?
How is distance measured on a contour map?