The Mercator projection is a way of flattening the round Earth onto a rectangular map so that any straight line drawn between two points gives you a constant compass direction. Created in 1569 by the Flemish cartographer Gerardus Mercator, it was designed to solve a very specific problem: helping sailors navigate the open ocean. It remains one of the most widely used map projections in the world, powering nearly every major online mapping service, but it comes with a well-known tradeoff. The farther you get from the equator, the more the map stretches landmasses, making places like Greenland look enormous compared to their actual size.
The Problem Mercator Was Trying to Solve
During the 1500s, global trade routes were expanding rapidly and sailors needed reliable maps. The challenge was fundamental: a globe is curved, but a navigation chart is flat. Existing flat maps couldn’t preserve compass directions consistently, which made plotting a course across the ocean unreliable.
Mercator’s solution was a cylindrical projection that made one crucial thing possible. If you drew a straight line between your starting port and your destination, that line told you the exact compass bearing to hold for the entire voyage. You could set your ship’s heading, keep it steady relative to north, and arrive where you intended. This type of route is called a rhumb line (or loxodrome). It isn’t the shortest path between two points on a globe, but it’s the easiest to follow with a compass, which mattered far more to a 16th-century sailor than saving a few miles.
Mercator titled his map “A New and Enlarged Description of the Earth with Corrections for Use in Navigation.” The name was apt. It genuinely revolutionized how ships crossed oceans.
How It Works
Imagine wrapping a cylinder of paper around a globe so it touches at the equator. The projection transfers every point on the globe’s surface onto that cylinder, then unrolls it into a flat rectangle. The equator maps perfectly, with no distortion at all. But as you move toward the poles, the math has to compensate for something: on the real Earth, the lines of longitude converge and meet at the poles, while on the cylinder they stay parallel and evenly spaced.
To keep directions accurate, the projection stretches the north-south spacing of latitude lines to match the east-west stretching that comes from forcing the longitude lines apart. This is what makes it “conformal,” a technical term meaning it preserves local angles and shapes. A small island near Norway will have the correct shape on the map. The coastline of Italy will look right. But the price of preserving those local shapes is that the scale changes dramatically from equator to pole. Objects near the poles get inflated in area, sometimes absurdly so.
Mathematically, the vertical coordinate increases according to a logarithmic function of latitude. As latitude approaches 90 degrees (the poles), that function shoots off toward infinity. This is why the Mercator projection literally cannot show the North or South Pole. The map would have to extend upward forever. In practice, most Mercator maps cut off somewhere around 80 to 85 degrees latitude.
How Size Gets Distorted
The distortion near the poles isn’t subtle. On a standard Mercator map, Greenland appears roughly the same size as Africa. In reality, Africa’s land area is about 30.4 million square kilometers, while Greenland covers just 2.17 million square kilometers. Africa is more than 14 times larger. Similarly, Alaska looks comparable to Australia on a Mercator map, but Australia is actually 4.5 times bigger. Madagascar appears to be about the same size as Great Britain, when it’s more than twice as large.
This happens because every landmass gets stretched by an amount proportional to how far it sits from the equator. Countries near the equator, like those in central Africa and Southeast Asia, are shown close to their true size. Countries at high latitudes, like Canada, Russia, and the Scandinavian nations, balloon outward. The effect is cumulative: Greenland sits between about 60 and 84 degrees north, so it gets stretched enormously in both dimensions.
The Political Controversy
Starting in the 1970s, German historian Arno Peters argued that the Mercator projection carried a political problem, not just a geometric one. Because the map inflates landmasses at high latitudes, Europe and North America appear disproportionately large compared to Africa, South America, and South Asia. Peters contended this visual distortion reinforced a Eurocentric worldview, making wealthier northern countries look dominant on the wall maps hanging in classrooms and government offices.
Peters promoted an alternative called the Gall-Peters projection, which preserves the relative area of all countries (Africa looks 14 times bigger than Greenland, as it should) but sacrifices shape. Continents near the equator appear vertically stretched, while those at high latitudes look squashed. The debate between Mercator and Gall-Peters became one of the most visible public arguments in cartography, spilling into education policy and international development circles. Neither projection is objectively “correct.” They simply preserve different properties, and the choice of which to use depends on what matters most for the task at hand.
Why Google Maps Uses It
Virtually all major online map providers, including Google Maps, Apple Maps, OpenStreetMap, Mapbox, and Esri, use a variant called Web Mercator. At first glance this seems like an odd choice, given all the criticism of Mercator’s size distortion. But the projection has practical advantages that matter enormously for digital maps.
First, it preserves direction. North is always straight up, no matter where you scroll on the map. For someone using a phone to navigate a city, that consistency is intuitive and useful. Second, the projection works extremely well at the local scale. When you zoom in to street level in any city on Earth, the shapes of blocks, parks, and coastlines are accurate. The size distortion only becomes a problem when you zoom out to view entire continents at once, which isn’t what most people use web maps for day to day.
Third, the rectangular grid tiles neatly. Digital maps are served as square image tiles that load as you pan and zoom. The Mercator projection’s rectangular geometry makes this tiling system straightforward to implement. It’s worth noting, though, that Web Mercator is a simplified variant of the original. Unlike the true Mercator, it treats the Earth as a perfect sphere rather than a slightly flattened ellipsoid, which introduces small errors. It’s not suitable for precise area calculations or spatial analysis, but for getting directions or browsing a map on your screen, it works well enough that it’s become the universal standard.
Alternatives and When They’re Used
No single map projection can preserve area, shape, direction, and distance all at once. Every flat map of a round planet requires a compromise. The Mercator projection prioritizes direction and local shape. Other projections make different tradeoffs.
- Equal-area projections (like Gall-Peters or Mollweide) show the correct relative sizes of countries but distort their shapes. These are useful for thematic maps showing population density, resource distribution, or climate data, where comparing the actual area of regions matters.
- Equidistant projections preserve true distances along certain lines, which is useful for measuring how far apart two specific locations are.
- Compromise projections (like Robinson or Winkel Tripel) don’t perfectly preserve anything but minimize distortion across the board. The Robinson projection is a common choice for wall maps and atlases because it “looks right” to most people, even though it’s technically imprecise in every dimension.
The Mercator projection endures not because cartographers think it’s the best representation of the world, but because it solved a real navigation problem in 1569 and then turned out to solve a real digital mapping problem 450 years later. Understanding what it distorts, and why, is the key to reading any world map with a critical eye.