The most widely used map in the U.S. today is the Mercator projection map. Mercator maps often appear in businesses, in libraries and in classrooms where geography is taught. This popularity is surprising, given the fact that the Mercator projection was first constructed in 1569, primarily for use by navigators.
The Mercator projections undeniable value to navigators stems from the fact that a straight line drawn by the traveler will have a constant compass bearing. This is accomplished, however, by spacing the parallels (lines of latitude, measuring North and South) in specifically increased amounts from the Equator to the poles, which results in an enlarging exaggeration factor of 33 past 80? latitude.
Courtesy of Ramona Currie
When the Mercator projection was created, the custom among map-makers was to place the map-makers countryin this case, Germanyat the center of the map. The Equator is placed 2/3 of the way down the map rather than halfway down. This arrangement depicts Europe as being larger than South America. In reality, South America is almost twice the size of Europe. Alaska is appears to be three times larger than Mexico, although Mexico actually is larger than Alaska. On a Mercator map, Greenland looks larger than China, even though China actually is four times larger than Greenland.
This distortion poses a significant limitation for any use other than navigation. Mercator projections present a surrealistic view of the world that makes them inappropriate choices for use in classrooms or in any application that compares separate regions of the world.
Projecting the Earth onto Paper
A globe is the most accurate representation of the Earth. This is true because it is impossible to create an absolutely accurate map by flattening out the Earths land masses. A classic example of this representation is to think of the Earths surface as the peel of an orangeeven small pieces of the peel will stretch and tear apart as they are flattened.
There are several ways to project the Earths surface to create a map (there are about 15-20 map projections in use today). Logically, a map user must be aware of which mapping properties remain accurate and which will be distorted in a particular projection. Typically, this choice will depend on the purpose and scope of the map. Each type of projection has its advantages and disadvantages. For example:
- A conformal map projection preserves the shape of small areas but distorts their size.
- An equidistant map projection shows true distances, but only from the center of the projection or along specific lines. For example, an equidistant map using the nations capitol as its center may show the correct distance between Washington, D.C. and Los Angeles, and between Washington, D.C. and Miami, but the distance shown between Los Angeles and Miami will not be correct.
- An equal-area map projection shows every part of the Earth at the same scale, all proportional to the surface of the Earth.
As you can now imagine, no flat map can be both conformal and equal-area, nor both equidistant and equal-area.
Equal-area map projections are generally used in studies of large areas to show relative distributions. For example, imagine a display of population density: if each million people are represented by a small dot, then it becomes important that each country appears in relative size to other countries, so that a dense collection of dots means a relatively dense population. In this situation, common in many classrooms, it makes no sense at all to use any other map than an equal-area map.
The Peters Projection Map
The Peters projection map was first introduced in Europe in 1974 by Dr. Arno Peters, a German historian and cartographer. Dr. Peters created his projection to aid in developing a realistic perception of the world. His equal-area projection corrects the Northern Hemisphere size bias of the Mercator map. All areas, both land and water, are of relatively proportional size: one square inch anywhere on the map represents 158,000 square miles on the Earths surface. The Peters projection wall map is a valuable educational tool because of its realistic portrayal of proportion.
As a comparison, a series of panels below show the Mercator map with the actual areas of continents labeled for comparison.
(c) 2002, Akademische Verlagsanstalt
Unfortunately, many Northern Hemisphere residents whose educational experience has been limited to the Mercator projection and similar presentations often are displeased with the different appearance of the Peters projection land masses. They feel more comfortable with the familiar Mercator projectioneven though the latters depiction of the world is unrealistic.
Inaccurate projections such as the Mercator map can send conscious or unconscious messages to geography students about the relative importance of countries and their peoples. Conversely, an equal-area map such as the Peters projection provides a far more realistic view of this planet. Moreover, this realistic presentation can send an important message to students: much of our understanding of the world has been based on the work of map-makers in the age of European domination.
Viewing Our World
The Mercator map has great value for navigation, but is not appropriate for teaching geography because it distorts the relative sizes of land masses. For teaching purposes, equal-area maps convey far more realistic illustrations of the world.
Those who are used to viewing Mercator projections will find that on an equal-area map, the land areas of the Northern Hemisphere may appear squashed compared to those on the Mercator map, but the fact remains that this equal-area illustration is far closer to reality than its popular predecessor, the Mercator projection.
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