The Mercator Map

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 projection’s 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

The Problem

When the Mercator projection was created, the custom among map-makers was to place the map-maker’s country—in this case, Germany—at 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 Earth’s land masses. A classic example of this representation is to think of the Earth’s surface as the peel of an orange—even small pieces of the peel will stretch and tear apart as they are flattened.

There are several ways to project the Earth’s 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 nation’s 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 Earth’s 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

www.Petersmap.com

(c) 2002, Akademische Verlagsanstalt

Perception Difficulties

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 projection—even though the latter’s 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.

For Additional Reading:

A New View of the World

Introduction to Map Projections

Maps and Man

Also:

The Peters Projection World Map was produced with the support of the United Nations Development Programme. For maps and other related teaching materials contact: ODT, Inc., PO Box 134, Amherst MA 01004 USA; (800-736-1293; Fax: 413-549-3503; E-mail: petersmaps@aol.com)