An interactive powerpoiint on reading & interpreting topographic maps.

1. Topographic Maps
Internet Interactive
Mr. Corner

2. Below is a Topographic Map
Contour line
Contour Interval

3. Contour Lines and Contour Intervals
• Contour Line: lines on topographic maps that
are of equal elevation.
• Contour Interval: difference in elevation
between two contour lines.

4. Aerial (top) View and Profile (side) View
Aerial (top) View Profile (side) view)
Click on either picture to see how a topographic map is made to make the contour line.

5. Completed Contour Map with Labeled
Contour Lines

6. Calculating the Contour Interval
• Find the difference
between 2 index
contours
2500-1250=1250
or
1250-0=1250
• Then Divide by 5
1250/5=250

7. Spot Elevations: elevations not exactly
on a contour line
• Point A falls between 0’ and
250’contours
• So its elevation is between 1’
and 249’
• (it’s not 0’ or 250’ because
those are exactly on the line!)
• You can estimate that since A
is drawn 1/2 way between
contour lines, its elevation is
halfway, or 125’

8. Any place inside a contour line is
HIGHER than the contour line...

9. Anyplace outside the contour line is
LOWER than the contour line

10. Contour lines are NEVER left out, so
on this map there is no elevation
600’ or less, OR 900’ or higher!

11. Hills and Valleys
• Hills are contour lines
in a series of circles
where the elevations
get higher
• Valleys are a series of
circles where the
elevations get lower
OR
Where contour lines
repeat

12. Lower contours not shown on the
map would appear if we made the
map larger...

13. Can You Determine
The Elevation? Click Picture.
• What is the contour
interval?______
• What is the Elevation
of points.
A ___________
B ___________
C ___________
D ___________
E ___________
F ___________
G ___________
H ___________
.G

14. Can You Label the
Contours? Click on
the Picture.
• Hints: You know the
contour interval is 40’
• Every contour line is a
multiple of the contour
interval (0,40,80, etc)
• You know the elevation
323’. Which 2 multiples of
40 does it fall between?
A______________
B______________
C______________
D______________
E______________

15. All contour lines eventually make a
circle. Sometimes only a part of the
circle shows on your map

16. So, is the elevation of contour line D
600’ or 700’?
Sometimes you just can’t tell

17. Sometimes there is a hint. Water
always flows downhill. There is a
river flowing thru Woodland
Valley. If D was
a hill (700’)then
the river flows
east, because
water can’t flow
uphill

18. The Rule of V’s
• Water always flows
from higher to
lower elevation
• contour lines make
a “V” shape when
they cross rivers

19. The point of the V always
points upstream--toward the higher
elevation
This river
is flowing
southwes
t

20. The V points upstream-and the river
flows the other way!

21. The “V” lets us know the elevation
of contour line D…..

22. The “V”
points west--
upstream, to
higher
elevation- so
the river
flows east, to
lower
elevation, so
D must be
600’

23. A Quickie Quiz. Click Picture.
• In which geographic
direction is the river
flowing?_________
• What is the elevation
of contour lines
A_____________
B_____________
C_____________

24. Relief
• Relief: is the difference in elevation between
the highest and lowest points in a region

25. No, we’re not done interpreting maps
yet...

26. Steepness: the closer together the
contour lines, the steeper the slope

27. Depressed? Got yourself
into a hole?

28. The volcano, with a crater in the
middle, rises above a flat plain.
The highest
elevation is at
the rim of the
crater. The
lowest point
of the volcano
is in the middle of the crater.
C.I.=200’

29. At the top of the volcano, the
contours go crazy...
…remember,
everything
inside the
contour is
supposed to
be higher
than the
contour!

30. But don’t get depressed...
Get depression contours!

31. Hachure marks
A depression
contour
shows a temporary
change in direction-
a “pothole”.
-Everything inside a
depression contour
is LOWER than the
contour

32. So, the topographic map
of the volcano should
look like this:
Rule: the first depression contour
repeats the elevation of the contour
line before it

33. The volcano’s topo map
Click 

34. A 3-D Look at Depression Contours
C-D is a “regular” valley
G-H is a “depression”: a temporary change in direction

35. Interpreting Depression Contours
Click on Picture
• Contour A _____
• Contour B _____
• Contour C _____
• Contour D _____
• Contour E _____
• Contour F _____
• Contour G _____
• Point q ________
• Point r _________
• Point w _________
• Point y __________

36. Contour Spacing and Steepness
• Steep Slope: when contour lines are close together.
• Less Steep Slope (gentle/gradual): when contour lines
are farther apart.
• Contours never touch or cross each other!

37. Steep and Gentle Slopes
Profile (side) view of an island
Aerial view of island showing contour lines
Closer together on the steepest side

38. Gradient
• Gradient tells you how steep your route is!
• It is the difference in elevation (ED) divided by the horizontal distance (HD):
 GRADIENT = ED/HD
• Take a look at this example:
• The vertical distance (here, the difference in elevation between points 'A' and
'B') = 10,000 feet
• The horizontal distance from 'A' to 'B' = 5 miles
• Gradient = vertical distance (elevation difference (ED)) divided by horizontal
distance (HD)
• The GRADIENT is 2000 feet per mile (10,000 feet divided by 5 miles)

39. Other Gradient Examples

40. Gradient Quiz Instructions
Click Picture to Take Quiz
• GRADIENT QUIZ INSTRUCTIONS
In the menu bar under "Select Line", click on "Scale".
• Click on the "Measure Line" button. A ruler will appear on the map.
• In the text box next to the question "One inch on map is equal to how many
miles?", type in your answer and click on the red check mark.
• Look in the bottom right 'response text area' for a response to your input.
• If your answer is not correct, follow the hint and try again.
• If the response is "Correct!", go to the menu bar again and click on "Line A-C".
Then, click on "Measure Line."
• Next, input an answer to indicate the "Distance on Map" and click on the red check
mark.
• If your answer is not correct, follow the hint and try again.
• If the response is "Correct!", input an answer to indicate "Actual Distance" and click
on the red check mark.
• If your answer is not correct, follow the hint and try again.
• If the response is "Correct!", input an answer to indicate "Elevation Difference" and
click on the red check mark.
• If your answer is not correct, follow the hint and try again.
• If the response is "Correct!", input an answer to indicate "Gradient" and click on
the red check mark.
• If your answer is not correct, follow the hint and try again.
• If the response is "Correct!", input an answer to indicate which of the illustrated
lines has a slope similar to the line whose gradient you have calculated. Then, click
on the red check mark.
• If your answer is not correct, follow the hint and try again.
• If your answer is correct, go to the menu bar and select the next line to work with.
• For curved lines, a straightened line and a ruler will appear in the box under the
map
• © 2002
Wayne G. Powell and David J. Leveson

41. Click on Either Picture to Practice
Labeling Contours

42. NOW...
We’re Done!

43. References
• http://academic.brooklyn.cuny.edu/geology/l
eveson/core/linksa/maptop.html