The Trouble with Maps
showing their coasts accurately. A Dutch
mapmaker, Gerhard Mercator, worked
out a way to do this in 1568. He used
complicated mathematical formulas to
keep the shapes of coastlines accurate
while showing all meridians as straight
ASIA
NORTH
ASIA
lines, the same distance apart at all
EUROPE
AMERICA
PACIFIC
latitudes. In fact, meridians are curved. A
ATLANTIC
OCEAN
degree of longitude is about 69 miles
OCEAN
AFRICA
wide at the equator, but all longitude
SOUTH
INDIAN
lines converge at the poles. So on a
AMERICA
Mercator projection, east-west distances
OCEAN
AUSTRALIA
are stretched as you go toward the poles.
And to keep shape and direction
accurate, north-south distances are
ANTARCTICA
ANTARCTICA
stretched in proportion.
The map on your classroom wall is most
ave you looked at the world map in your
likely a Mercator projection. It was the most
classroom lately? Chances are, it shows
useful way of representing the world for nearly
Canada as twice as big as the United States, even
300 years. A sailor or pilot can plot a course
though the two countries are actually about the
between two points on a Mercator map just by
same size. Greenland may appear about the same
drawing a straight line between them and
size as Africa. In fact, it’s only about onechecking the compass direction.
fourteenth as large. And Antarctica is a jagged
It wouldn’t necessarily be the shortest course,
strip at the bottom—if it appears on the map at
however. That’s because the shortest distance
all. Why would you have such an inaccurate map
between two points on the Earth’s surface does
in your classroom? What’s the use of such a map?
not appear as a straight line on a Mercator map.
In fact, sailors have been using maps like this
It’s a curve that connects two points on the edge
for over 400 years. They plot courses on such
of an imaginary circle passing through the center
maps to this day, and so do airplane pilots. But
of the Earth. Navigators call it a great circle
it’s only one of several possible ways of showing
route.
the world on a map.
Does this seem odd? Just remember the
The trouble with maps is that they’re flat, but
difference between a map and a globe. If you
the world isn’t. Ptolemy recognized this problem
stretch a piece of string across a globe from San
nearly 2,000 years ago. When you make a map,
Francisco, California, to Tokyo, Japan, you’ll see
you’re projecting a curved surface onto a flat one.
the great circle route between the two cities. And
You can’t accurately show size, shape, and
you’ll know why a ship bound on that route
distance all at once. For that, you need a globe.
would first set a course northwest, toward Alaska.
Choosing what kind of projection to use for a
An azimuthal projection shows distances
map depends on what the map will be used for.
between places accurately. On such a map, a
Sailors in the 16th century needed a map on
great circle route is a straight line. But it’s of
which they could plot a compass course. They
little use for setting a compass heading. And the
didn’t care about the relative sizes of continents
farther you get from the center, the more
and islands. But they cared very much about
distorted the continents and oceans appear.
ARCTIC OCEAN
H
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Content Reading
ARCTIC
OCEAN
Put an X in the square beside the best answer.
1. The Mercator projection is named for ______.
䡺 a Dutch mapmaker
䡺 a Portuguese explorer
䡺 an English ship
䡺 an island near Africa
2. This article is mostly about ______.
䡺 map projections
䡺 Mercator’s map
䡺 how globes are made
䡺 how navigators plot a course
3. The captain of a ship sailing a great circle route ______.
䡺 sets the course on a Mercator projection
䡺 always starts out sailing northwest
䡺 must often reset the compass course
䡺 is giving up speed for a safer voyage
4. The Mercator projection was invented ______.
䡺 before Ptolemy wrote about maps
䡺 after Columbus reached America
䡺 before the compass was invented
䡺 after the entire world had been mapped
5. Because a Mercator map shows meridians as straight lines, ______.
䡺 it’s useful for plotting great circle routes
䡺 a degree of longitude is 69 miles wide
䡺 the shapes of coastlines are accurate
䡺 distances appear stretched near the poles
6. In paragraph 4, the word converge means ______.
䡺 become smaller
䡺 get colder
䡺 spread apart
䡺 come together
Write your answer to the following question on the lines below.
A pilot is flying the shortest route from Los Angeles, California, to Rome, Italy. In what direction
would she head first? What countries would she fly over? How could you check your answers?
Geography
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