Map Projections and Distortion - Mercator, Gall-Peters

World map printed as narrow globe gores showing how the curved surface of Earth can be separated into slices and flattened onto a flat page. — These narrow slices are called gores. Globe gores can flatten the Earth with very little distortion because each slice covers only a small part of the curved surface. The slices wrap smoothly around a sphere, but gaps appear when they are laid flat on a page.

When you look at a tennis ball, you can only see part of it at a time, even if you turn it around in your hand. To see the entire ball at once, you would have to flatten it by applying enough force so that the sides would split and its round shape would change. It might still be fuzzy and yellow, but it would no longer be a ball. The same thing would happen if you tried to create a map of the world. You must flatten a globe into a flat map to view the entire surface.

Distortion on Flat Maps

A round globe can accurately show size, shape, distance, and direction, but turning it into a flat map requires stretching some areas of the map. Mapmakers call this stretching distortion.

Illustration showing how a cylindrical map projection transfers features from a globe onto a flat map by projecting the Earth’s curved surface onto a surrounding cylinder. — Modern map projections use sophisticated algorithms to preserve accuracy in area, direction, and distance. But in its simplest form, the idea is to project a round image onto a flat surface.

For over 400 years, mapmakers have used mathematics to develop algorithms that help them project the globe onto a flat surface. An algorithm is simply a set of rules for solving a problem.

Flat world maps use algorithms to produce projections. A map projection is a way to represent the Earth on a flat surface. All flat maps have distortion, so shape, distance, direction, and land area can never be completely accurate. This distortion is a trade-off we accept because different map projections meet different needs.

Mapmakers use many projections because all flat maps have some distortion. Some projections are better than others at serving different needs, but because every map is at least a little bit wrong, there is no one best map projection.

Mercator’s Map

Mercator Projection world map showing severe enlargement of Greenland, Antarctica, and other regions near the poles compared with areas closer to the equator. — Most people think Greenland and Africa are about the same size because they are most familiar with the Mercator Projection. In reality, Africa is about 13.7 times larger than Greenland. To preserve direction, the Mercator Projection stretches areas near the poles and compresses areas closer to the equator.

In 1569, Gerardus Mercator created a map where parallels and meridians cross at right angles. Mercator’s map is excellent for navigation because it clearly shows direction. It is used by Google Maps and is likely the image you have in mind when you think of a world map, but the Mercator Projection introduces significant distortion. This is because, to get the parallels and meridians to cross at right angles, Mercator created an algorithm that stretched areas closer to the poles and squeezed those closer to the equator.

Equal Area Maps

An equal area map displays the sizes of things more accurately than a Mercator Projection. The Gall-Peters Projection is one of several equal-area projections. Gall-Peters sacrifices accuracy of angle and shape to show land area more accurately. Compare Greenland and Africa on the two projections. Africa is fourteen times larger than Greenland. The Gall-Peters map shows this more accurately, but on a Mercator Projection, the two landmasses appear to be about the same size.

Gall-Peters Projection world map showing land areas at approximately correct relative sizes, making Africa appear much larger than Greenland compared with a Mercator Projection. — The Gall-Peters Projection may look wrong if you are more familiar with Mercator-style world maps. But Gall-Peters shows the relative sizes of land areas more accurately than the Mercator Projection, including the fact that Africa is nearly fourteen times larger than Greenland.

The Winkel Tripel Projection

Some maps use very sophisticated mathematics to combine the advantages of the Mercator Projection and equal area maps. The Winkel Tripel Projection attempts to minimize distortion. The German word Tripel, meaning triple, is in the title because the map prioritizes accuracy in area, direction, and distance. The National Geographic Society uses the Winkel Tripel Projection for many of its maps.

Winkel Tripel Projection world map showing curved parallels and meridians designed to reduce distortion of size, shape, and distance across the Earth’s surface. — The Winkel Tripel Projection attempts to take the best features of the Mercator Projection and equal-area maps. It is a sophisticated compromise designed to minimize distortion in area, direction, and distance.

There is No Perfect Flat Map

They Only Look Like Rectangles

Wyoming and Colorado look like rectangles on a map, but because of the curvature of the Earth, their northern borders are slightly shorter than their southern borders. For most purposes, calling the states rectangles is fine, but if you get very technical, geometrists call this shape an isosceles trapezoid. Wyoming’s southern border is about 23 miles longer than its northern border, while Colorado’s southern border is about 22 miles longer. And if you measure even more carefully, the truth becomes stranger still…

Legally, It’s a Hexahectaenneacontakaiheptagon

When Colorado became a state, surveyors physically marked the borders on the ground. Their 19th-century equipment could reliably create only short straight segments, so the legal border contains hundreds of tiny deviations rather than four perfect lines.

A 697-sided polygon is called a hexahectaenneacontakaiheptagon. Mathematicians build the word from Greek roots:

• hexahecta means 600
• enneaconta means 90
• kaihepta means 7

Put together, it means a 697-sided polygon—a word unlikely to appear in a spelling bee because it is nearly impossible to pronounce.

Resources

Download this lesson as
Microsoft Word file or as an
Adobe Acrobat file.

Mr. Donn has an excellent website that includes a section on Geography.

Cite this page:
Dowling, Mike, “Map Projections: Flattening the Earth,” mrdowling.com, September 17, 2026. Web. [Date of access].

Sources:
Mark Monmonier, Rhumb Lines and Map Wars: A Social History of the Mercator Projection (University of Chicago Press, 2004)
Arno Peters, The New Cartography (Friendship Press, 1983)
New Mexico v. Colorado, 267 U.S. 30 (1925)

NEXT

The Six Essential Elements of Geography

EXPLORE