Topographic maps use contour lines to represent the shape and elevation of land. Contour lines connect points of equal elevation and never touch or cross. Closely spaced lines indicate steep slopes, while widely spaced lines show gentle slopes. A contour interval is the elevation difference between lines. Topographic maps also use colors, symbols and labels to depict features like water, vegetation and man-made objects. Benchmarks provide exact elevation references and are marked on maps with their altitude in feet.

1. Topographic Maps

2. Lesson Objectives
 Define a topographic map and state
its uses.
 Describe how contour lines show the
elevations, shape, and slope of the
land.
 Identify the meanings of some
symbols and colors used on
topographic maps.

3. What is a topographic map?
 A topographic map, also known as a
contour map, is a map that shows
the shape of the land using contour
line.
 It is a map that shows and elevation
field, meaning how high and low the
ground is in relation to sea level.

4. 09_01.JPG
- Quadrangle maps are published in several sizes, but two are most
common: 15-minute quadrangle maps and 7½-minute quadrangle
maps. (For example, a 15-minute map represents an area that
measures 15 minutes of latitude by 15 minutes of longitude.)

5. What are contour lines?
 Contour lines are lines that connect
points that are of the same
elevation.
 They show the exact elevation, the
shape of the land, and the steepness
of the land’s slope.
 Contour lines never touch or cross.

6. What is a benchmark?
 A benchmark is a point where exact
elevation is known and is marked
with a brass or aluminum plate. It is
marked BM on the map with the
elevation numbers given in feet.
 Benchmarks are useful to help
determine contour lines.

7. Other Topographic Terms
 Map scale – compares distances on
the map with distances on earth.
 Legend – explains symbols used on
the map.
 Index contours – contour lines that
are labeled to help you find the
contour interval.

8. Topographic Maps
SCALE (ON MAP) (ON GROUND)
1 : 24,000
1
24,000
“1 to 24,000”
1 pencil = 24,000 pencils
1 centimeter = 24,000 cm
1 inch = 24,000 in
1 inch = 2,000 FEET

9. What is a contour interval?
 A contour interval is the difference in
elevation between two contour lines
that are side by side.
 Remember that a contour interval is
not the distance between the two
lines – to get the distance you need
to use the map scale.

10. 09_05.JPG
A contour line is drawn where a horizontal plane (such as A, B, or C) intersects the
land surface. Where sea level (plane A) intersects the land, it forms the 0-ft contour
line. Plane B is 50 ft above sea level, so its intersection with the land is the 50-ft
contour line. Plane C is 100 ft above sea level, so its intersection with the land is the
100-foot contour line. D is the resulting topographic map of the island. It was
constructed by looking down onto the island from above and tracing the 0, 50, and
100-ft contour lines. The elevation change between any two contour lines is 50 ft, so
the map is said to have a 50-ft contour interval.

11. What if my contour lines are close
together?
 If the contour lines are close
together, then that indicates that
area has a steep slope.

12. What if my contour lines are far
apart?
 If the contour lines are far apart,
then that indicates the land has a
gentle slope (low slope).

13. What do the dark colored contour
lines mean?
 The dark colored contour lines
represent every fifth contour line to
make it easier to read the map.

14. What do depressions in the map
look like?
 A depression, such as the inside of a
dead volcano, is represented by
Hachure lines.
 Hachure lines are regular contour
lines with small segments sticking
out from it.
 The first hachure line is at the same
elevation as the contour line before
it.

15. More on Contour Lines
 Contour lines form V’s that point
upstream when they cross a stream.
 It is important to remember that
they point in the opposite direction
as the flow of water.

16. What do the colors on the
topographic map represent?
 Blue lines/shapes - represent water
features, such as streams and lakes.
 Brown – contour lines
 Black – Roads, buildings, railroads,
other man made objects.
 Green – Woodland areas
 Red - Highways

17. Now that I know what a
topographic map is, how do I read
it?
 First determine the contour interval
(the distance between each contour
line)
 Then determine the map scale
(usually at the bottom of the map)
 Identify any hills or depressions
 Use the legend to identify man made
features.

18. Reading a topographic map cont.
 Look for areas where the contour
lines are close together – they
indicate a steep area.
 Look for areas where the contour
lines are spread apart – they indicate
a gentle slope.

20. 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?