1. Introduction to Topographic Maps + Contour Lines

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

3. Topographic Maps A. Contour Line:
line on a map that connects points of EQUAL elevation.
shows elevation and shape of the land
Relief - Difference between high and low elevations

5. Topographic Maps B. Contour Interval –
Difference in elevation between each line.
MUST be separated by same interval.
Contour interval =
20 feet
520
540
560
580

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

7. Let’s take a walk up a hill!

8. We’re now at an elevation of 100 feet.
Draw + label on your map – 100’
Contour lines
100 ft

9. Now we’re at 200 feet. Contour lines 200 ft 100 ft
Draw + label on your map – 200’
Contour lines
200 ft
100 ft

10. We’ve made it to 300 feet! Contour lines 300 ft 200 ft 100 ft
Draw + label on your map – 300’
300 ft
200 ft
100 ft

11. We’re on the peak, but what’s our elevation?
300 ft
Contour lines
200 ft
100 ft

12. Add contour lines for every 50 feet and see if that helps.
Any ideas?
Add contour lines for every 50 feet and see if that helps.
300 ft
200 ft
100 ft

13. We know that we are above 350 ft, but less than 400 ft.

14. Let’s now look at the same hill, but the way we might see it from an airplane.

15. Each color change represents a 50-foot change in elevation.

16. Now, let’s try the same hike! Our elevation is 0 feet.

17. Now, we are at the peak, elevation between 350’ – 400’.

18. Imagine the sea level rising steadily
Imagine the sea level rising steadily. Those would be our contour lines = lines of same elevation.

21. 500’ upward What is contour interval?
“Real World”
500’
Do the contour lines bend upward or downward at a stream?
Contour Map
upward

22. 2. Rules for Contours
Contour lines never cross

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

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

26. Rules for Contours
The maximum possible elevation for a hill is 1 less than what the next contour “should” be.
--OR--
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

27. 399
239

28. 5. Closely Spaced Contours
Closely spaced contours = steep gradient.

30. 6. Widely Spaced Contours
Widely spaced contours = gentle, gradual gradient.

32. A A B B

33. Add gradient to your map

35. 7. 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. Draw a hachure mark
The elevation of the first depression contour is the same as the lowest regular contour near it.

36. Rules for Contours
d. The lowest possible elevation for a depression is 1 more than what the next contour “should” be.
-- OR --
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

37. 100
100 50

38. 8. 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.

40. Map Scales
Indicates the distance on the map compared to distance in the real world
3 types:
1. Graphical - a line divided into equal parts and marked in units of length.

41. Map Scales
2. Fractional – Expressing distance as a ratio. Example 1:63,360
This means: One unit on the map equals 63,360 units in the real world.
(Fyi…there are 63,360 inches in a mile)

42. Map Scales 3. Verbal– expressing distance as a statement.
Example: Saying aloud, 1 cm on the map = 1 km in the real world.

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44. 4. Gradient The steepness of a slope between any 2 points on a map.
Change in elevation
Distance

45. 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

46. What is gradient between points A and B?
Change in elevation
Contour Interval = 20 ft
Distance B
2250 ft / 6 miles A
= 375 ft/mile 6
miles 2 4 8 10