Why Every Flat World Map Distorts Something

A globe represents Earth as a curved surface. A paper map is flat. To move information from one to the other, cartographers use a mathematical system called a map projection. Imagine peeling an orange and pressing the skin flat. It tears, overlaps or stretches because a curved surface cannot become a flat sheet without change.

Map projections solve this problem in different ways. Some imagine projecting Earth onto a cylinder, cone or flat plane. Others use more complex calculations. Each method creates a useful map, but none escapes distortion. The important question is not whether a projection distorts. It is what it distorts and whether that trade-off fits the map's purpose.

Distortion is usually smallest near the places where the imagined projection surface touches or cuts through the globe. It grows farther away. This is why a map may represent one region well while making distant areas look increasingly strange.

A conformal projection preserves local shapes and angles reasonably well, which can help with navigation. However, area may become badly distorted. The familiar Mercator projection makes regions near the poles look much larger than they really are. Greenland appears enormous beside Africa even though Africa has vastly more land area.

An equal-area projection protects relative area, making it useful when comparing forests, populations or countries by size. Shapes may look stretched or compressed. Other projections focus on distance from a certain point, direction along selected routes or a balanced appearance for general reference. A projection suited to airline routes may be a poor choice for comparing country sizes, and a classroom map may favour visual balance over any single measurement.

No projection is neutral in every situation. A map centred on one region may make it feel visually important. A projection that enlarges high latitudes can quietly change how viewers imagine the size of countries. Cartographers choose projections for practical reasons, but readers should still notice the choices.

You do not need to distrust every map. You need to ask what job it was designed to do:

• •Check the projection name if it is provided.
• •Compare suspicious sizes with a globe.
• •Notice which areas are stretched near the edges.
• •Use equal-area maps for land-size comparisons.
• •Remember that map centres and borders are choices.

If you have ever watched a flight tracker, you may have noticed that a plane from Europe to the west coast of North America seems to swing far north, sometimes passing over Greenland or northern Canada. On a flat map this looks like a long detour. In reality it is close to the shortest possible path. On a sphere, the shortest route between two points follows a great circle, which is any circle whose centre is the centre of the Earth, like the equator or a line of longitude.

Most projections cannot show great circles as straight lines, so the shortest routes appear bent. You can check this yourself with a globe and a piece of string. Stretch the string tightly between two distant cities and notice how it passes much closer to the pole than a straight ruler line on a paper map would suggest. Real flight paths also adjust for winds, airspace and safety rules, but the basic curve comes from geometry. A special gnomonic projection does show every great circle as a straight line, at the cost of severe distortion elsewhere.

Gerardus Mercator published his famous projection in 1569 for sailors, not for classrooms. Its key property is that a line of constant compass bearing, called a rhumb line, appears as a straight line on the map. A navigator could draw a straight line from port to destination, read off the angle and hold that course with a compass. The route is not the shortest, but it is simple to follow, which mattered greatly before modern instruments.

Problems arose when the projection became a general wall map, shaping how people pictured the size of continents. In the 1970s the historian Arno Peters promoted an equal-area projection, now often called Gall-Peters after an earlier version by James Gall, arguing that Mercator exaggerated rich northern countries. Many cartographers agreed with his criticism of Mercator while objecting to his map's heavily stretched shapes and his claims of novelty. Today many web maps use a version of Mercator because it keeps local shapes and angles right when you zoom into streets.

In the nineteenth century the French mathematician Nicolas Auguste Tissot devised a simple way to show what a projection does. Imagine drawing identical small circles at regular points all over a globe, then projecting the globe onto a flat map. Where the map keeps local shapes, the circles stay circles. Where it stretches more in one direction than another, they become ellipses. Where it changes area, they grow or shrink. These diagrams, called Tissot's indicatrices, let you compare projections at a glance and turn the trade-offs of map-making into something you can actually see.

On a Mercator map the circles stay round but grow steadily towards the poles. The stretch in every direction at a given latitude equals one divided by the cosine of that latitude. At 60 degrees north, roughly the latitude of Oslo and the southern tip of Greenland, the cosine is one half, so distances are doubled and areas appear four times too large. Further north the exaggeration grows even faster, which is why Greenland, at around 2.2 million square kilometres, looks comparable to Africa, which covers about 30 million, roughly fourteen times as much. At the poles the scale becomes infinite, so Mercator maps simply cut them off.

Since no projection can preserve everything, many general-purpose world maps aim for a compromise, allowing a little distortion of every kind rather than a lot of any one. The Robinson projection, designed in the 1960s by the American cartographer Arthur Robinson, was chosen to look right to the eye rather than to satisfy a single mathematical rule. The National Geographic Society adopted it for its world maps in 1988, then switched in 1998 to the Winkel tripel projection, which keeps errors in area, angle and distance all fairly low. Neither suits precise measurement, but both avoid the extreme stretching of Mercator.

Another strategy is to cut the map. Interrupted projections split the globe along lines that matter little for the map's purpose, much like slicing orange peel into segments so it lies flatter. The Goode homolosine projection, published by John Paul Goode in the 1920s, makes its cuts through the oceans, so the continents keep their true relative areas with less shearing of their shapes. In the 1940s Buckminster Fuller went further, unfolding the globe onto the faces of a polyhedron to make his Dymaxion map, which shows the continents as one almost continuous landmass. The price is gaps and unfamiliar layouts.

Every flat world map trades one kind of accuracy for another. Shape, area, distance and direction cannot all remain perfect at once. Learn what a projection protects, and a map becomes more useful because you understand both its strengths and its limits.