Graphing a Geographic Transition:
from Equatorial Rainforest to Tropical Desert
The climate of Africa can be described as a gradual transition from
rainforest to desert. A place midway between the Equator and
Tropic of Cancer gets less rain than the Equator, because it does
not have as many days when
the Equatorial Rainy Belt
30
is overhead.
10
In short, one of the most
important geographic facts
about any place in Africa is
the number of rainy
days per year at that place.
One very useful way
to visualize the pattern
of rainy days in Africa
is to make a graph that
shows the number of
rainy days at different
latitudes.
10
30
E QUATOR
Here is a fast way to make a graph
of that kind from a map.
60
100
180
100
60
30
10
1.
Make a graph grid that matches
the scale of the map. We have
done that for you on this page.
2.
Place the grid on the map with the zero-line on the line
you wish to graph. Again, we have done that on this page.
3.
Note what the map says for places that are located at
different latitudes (different distances away from the Equator).
4.
Mark those values (in this case, rainy days) at the appropriate
place on the graph on the next page.
(We have started the graph by doing four places.)
©2012 P Gersmehl Teachers may copy for use in their classrooms. Contact [email protected] regarding permission for any other use.
Graphing a Geographic Transition:
From Equatorial Rainforest to Tropical Desert
The climate in Africa can be described as a gradual transition from rainforest to desert. A
place midway between the Equator and Tropic of Cancer gets less rain than the Equator,
because it does not have as many days when the Equatorial Rainy Belt is overhead. In
short, one of the most important geographic facts about any place in Africa is the number
of rainy days per year at that place.
One very useful way to visualize the pattern of rainy days in Africa is to make a graph that
shows the number of rainy days at different latitudes.
Use the information from the map to finish this graph by adding dots for 6 more places,
scattered all the way from 30°N to 30°S. You might look for places where lines on the map
cross the grid zero-line. Then connect the dots with a smooth line.
R
A
I
N
180
150
120
Y
90
D
60
A
Y
S
30
0
30 oN
20 oN
10 oN
equator
10 S
L A T I T U D E
20 S
30 S
Once you have a graph like this, you can add another line that shows the transition for
another kind of information, such as population density or income. That makes it easier to
compare different kinds of information.