Why Is Mercator’s Projection Important?
Gerardus Mercator (5 March 1512 – 2 December 1594) was a 16th-century geographer, cosmographer and cartographer from the County of Flanders. He is most renowned for creating the 1569 world map based on a new projection which represented sailing courses of constant bearing (rhumb lines) as straight lines—an innovation that is still employed in nautical charts. Mercator’s projection is important to geographers because, unlike other projections, a straight line drawn on it gives a true compass bearing.
A projection is simply
a means of transferring a round section of the world on to a flat sheet of
paper. This is more easily said than done, for, no matter how hard you try, you
cannot do it without altering the shapes or sizes of countries or the distances
between them. You can try this for yourself. Draw a rough map of the world on
an orange with a felt tip pen, then cut the orange into sections. When you have
eaten the orange, try to arrange the curved pieces of peel into a flat map. You
can see that if the lands by the Equator, or the widest parts of the orange
peel, are touching, there are large gaps to the north and south. To make a map
in which there are no gaps, it is necessary to stretch these lands in the north
and south—and this is just what Mercator did.
The history of projections goes back to the Greeks who realized as long ago as 500 B.C. that the world was round. Eratosthenes, a Greek who lived at Alexandria in the 2nd Century B.C. even calculated the circumference of the world to be 25,000 miles. His estimate was only a little more than the correct distance which is 24,901.8 miles at the Equator.
Mercator’s projection increases the distances between the lines of latitude (the lines parallel to the Equator) as one moves further north or south. While this makes the map useful for navigation, it also gives people many wrong ideas about the world. It makes some countries, such as Greenland appear too large. The areas of land at the Equator on Mercator’s projection are correct. But those at 45 degree North or South are doubled, and those at 75 degree are nearly 16 times too large.
Practically every marine chart in print is based on the Mercator projection due to its uniquely favorable properties for navigation. It is also commonly used by street map services hosted on the Internet, due to its uniquely favorable properties for local-area maps computed on demand. On the other hand, because of great land area distortions, it is not well suited for general world maps. Therefore, Mercator himself used the equal-area sinusoidal projection to show relative areas. However, despite such distortions, Mercator projection was, especially in the late 19th and early 20th centuries, perhaps the most common projection used in world maps, despite being much criticized for this use.