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Adapted from The
Book of Where, N. Bell
Bonnie Murray
Jo Mackey Magnet school
2726 Englestad
North Las Vegas, NV 89030
702.799.7139
ASGI 1995
OVERVIEW
This activity will aid students in understanding
why and how mapmakers represent a 3-dimensional globe on a 2-dimensional
map.
GRADES
Grades 2 - 5, but adaptable to all grade levels.
STANDARDS
 #1 How to use maps
and other geographic representations, tools, and technologies
to acquire, process, and report information from a spatial perspective.
TIME
One hour to 90 minutes.
MATERIALS
- One or more globes, including an inflatable
if available.
- One or more world maps, including at least
one Mercator projection.
- One grapefruit or orange for every 2 - 4
students, plus one for the teacher.
- One permanent black felt marker, plus one
for every 2 - 4 students if desired.
- One blank Venn Diagram
on a transparency for whole group discussion.
- Overhead marking pens.
- Paper towels.
- One kitchen knife for the teacher's use.
OBJECTIVES
A. To compare and
contrast world maps and globes, including a study of the shapes
and sizes of continents and oceans on both.
B. To convert a 3-dimensional
globe to a 2-dimensional map.
C. To introduce the Mercator
map projection.
D. To observe map distortions
of shape, area, distance, direction and angle.
PROCEDURES
1. Set up student
workstations including a world map, globe, grapefruit, and paper
towels. One black permanent marker per group is optional (see
Step #8 below). If you prefer, have all materials in one central
location and assign a "getter" for each group to get
the materials before beginning the lesson.
2. Begin by defining guidelines
for cooperative learning groups. Review guidelines already established
in your classroom or introduce them to "Harmony" by
having them discuss each behavior and what the results will be
if they follow these guidelines:
- Listen
- Appreciate
- Communicate
- Yield
- Concentrate
- Control Yourself
3. Explain that it
has taken centuries for people to get a complete picture of the
world in which we live. Until the time of Magellan, most people
believed that the earth was flat. They used flat paper to represent
the location and shape of water and land. After Magellan circled
the earth in 1519, he proved that the earth was round. Then cartographers,
or mapmakers, had to place land and oceans on a round globe to
be accurate. Unfortunately, one can only see half of a globe
at a time. A globe is also hard to carry around and doesn't fit
into books! Cartographers had to find a way to "peel"
the globe so that they could fit their pictures of it onto a
sheet of paper again.
4. Invite the students
to look at the globes and maps in the classroom and share their
thoughts about how they are alike and different, in overall appearance
and between specific continents. Record their ideas on the Venn
Diagram transparency (see example of
completed Venn Diagram).
5. Ask the students
to suggest ways in which a globe could be flattened to be an
accurate map of the world. If you have an inflatable globe, let
the air out of it to show them that this particular solution,
which they are certain to suggest, is not possible.
Hold up a grapefruit and ask the students what
shape it is (sphere, globe). Compare the shape to one of the
globes in the classroom. Demonstrate how the land masses and
oceans fir onto the grapefruit globe by drawing them on with
a black permanent marker while the students watch.
6. Explain to the
students that they will have an opportunity to try to flatten
a global grapefruit with a cooperative group. Now is a good time
to discuss proper use of the materials with the students and
remind them to use the guidelines for working in cooperative
groups.
7. OPTIONAL: Teachers
of older students may want to have the groups draw the land masses
and oceans on their grapefruit before beginning to peel them.
8. Have the students
meet at their cooperative group workstations. First they will
brainstorm ways of flattening the grapefruit. Then they will
decide on which method they wish to try. Now it's time to get
messy!
9. Circulate to listen
in on each group's conversations, to keep them on task, and to
monitor their progress.
10. After most groups
have finished their tasks, invite the class back together as
a whole group so that each cooperative group can share its flattening
procedure, successes, and frustrations.
11. Use a knife to
split the skin of your global grapefruit from each "pole"
to the "equator," leaving the segments connected at
the equator by about 1/2 inch, demonstrating how a spherical
object can be split to flatten it. Press your grapefruit skin
flat and ask the students what happened to the continents and
oceans (they got cut in places).
12. Explain that at
first cartographers had to "connect the dots" or stretch
areas where land masses and oceans are split. Over 400 years
ago, a cartographer named Gerhard Kremer who used the name "Mercator"
on his maps, found a way to use light and shadows to project
the globe onto a cylinder and then to turn that cylinder into
a flat surface for a map. Most of the early maps you see of the
whole world are Mercator projections which were used extensively
for navigation in the past. The easiest way to tell if a map
is a Mercator is by looking at the latitude and longitude lines.
If they form perfect rectangles (all latitude and longitude lines
meet at right angles), the map is a Mercator projections. Older
students can look at their Mercator projection maps and discuss
whether the distortions are in shape, area, distance, direction,
or angle. No single map can perfectly represent a globe, so students
need to be able to determine which characteristic is being distorted
in the map that they are using.
13. Have all the groups
clean up their work stations and dispose of any waste. They may
want to eat the grapefruit segments that haven't been destroyed
in the process of flattening the skin.
EXTENSIONS
1. Read the book Maps
and Globes, by Jack Knowlton. It has a simple but solid
description of the history and types of maps and globes.
2. Have the students
blow up round balloons, cut out correctly-sized and -shaped continents,
then draw in the latitude and longitudes lines with permanent
marker. From here, instruct them in the technique for projecting
a globe onto a Mercator grid so they can experiment with turning
their balloon globe into a flat map.
3. Show the students
examples of various projections (Robinson's, which was designed
to minimize all types of distortions, or Peter's) so they can
compare and contrast the size and shape of the land masses and
oceans with those on a Mercator projection. Older students may
be able to determine if the shape, area, or distance of land
masses and angle and direction of longitude and latitude lines
on each type of projection remains the same as a globe.
RESOURCES
- Bell, Neill, The
Book of Where, Little, Brown and Company, Boston, 1982.
- Knowlton, Jack, Maps
and Globes, Harper Trophy, New York, 1985.
- Geography for Life: National Geographic Standards, National Geographic Research and Exploration, Washington,
D.C., 1994.
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