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Gerardus Mercator revolutionized mapmaking. He was almost executed for it.

A portrait of Gerardus Mercator.
A portrait of Gerardus Mercator.
Stock Montage/Getty Images

Even if you've never seen Gerardus Mercator, you've almost certainly seen his work. His Mercator projection map, invented in 1569, was the primary map that navigators used for years. It's the form that many maps still come in today. And the name he chose for his massive collection of maps — "Atlas" — is widely used.

That's why today, on what would have been his 503rd birthday, he's being celebrated worldwide (including with a Google Doodle that shows him hard at work on a globe).

Yet Mercator wasn't always so widely appreciated. At one point, his passion for geography almost got him killed.

Why Mercator's maps were such a huge deal

Today we're so familiar with the Mercator projection that it's easy to forget how revolutionary it was at the time. Mercator created his maps by meshing his technical expertise making globes with mathematical insights.

Mercator was born to a shoemaker on March 5, 1512 in Rupelmonde, Flanders (the Belgian town is about 15 miles from Antwerp). His uncle enrolled him at a monastic school, and Mercator quickly developed the good penmanship that served him well as a mapmaker. In 1530, he enrolled in the University of Louvain, where he studied mathematics while further exploring maps.

In the 1500s, globe-making was a precise and difficult art. Mapmakers often etched their maps onto paper that they then painstakingly pasted onto paper mache spheres. Old maps had problems, however. Mapping a three-dimensional globe onto a two-dimensional map always involves some distortions, but early maps had serious issues for navigators. They were mostly elliptical and struggled to capture the curvature of the Earth for sailors who were plotting a course. Sailors using them were constantly twisting, curving, and recalculating to compensate for their maps' deficiencies.

In 1569, Mercator developed a better, more accurate projection. Although the execution was difficult, the basic idea was simple: Imagine a globe with a paper cylinder wrapped around it — Mercator projected that globe onto the paper and then unwrapped it. He then expanded degrees of latitude as they approached the poles, which distorted land, but allowed the directions to be clearer.

A cylindrical projection.

A cylindrical projection model. (Wikimedia Commons)

His new map was a revelation, because the projection kept the latitude and longitude lines at consistent 90 degree angles. These clean angles made it easier for sailors to plot their course without constantly adjusting for mapping mistakes. It was also easier to see the relationships between landmasses. (The downside was that it distorted the size of some of the land masses, particularly near the poles.)

Mercator's projection

Mercator's 1569 map. (Wikimedia Commons)

That achievement was followed by the publication of Mercator's Atlas. Though it wasn't the first book of maps, the name Mercator chose came to define the type of book.

Mercator's mapmaking almost cost him his life

Mercator's most famous projection almost never happened, because 25 years earlier he was imprisoned and nearly executed.

Because Mercator corresponded frequently with distant friars and traveled often — gathering information for his maps — local authorities in Louvain accused him of heresy as a suspected Protestant. Since maps were so new, and because many countries were at war, mapmakers had to travel far and wide to gather information, which led to accusations of espionage or heresy. Mercator and many of his university contemporaries were jailed in 1544.

Four of the people imprisoned alongside Mercator were executed, and Mercator spent seven months in jail before he was released. It's unclear if Mercator was actually a Protestant sympathizer or just a nomadic mapmaker, but he eventually was released from prison and, with the help of his sons and correspondents abroad, he returned to making maps.

Despite criticisms, Mercator's legacy persists

In recent years, the Mercator projection has come under fire for distorting the real shape of the world's continents — objects closer to the poles appear larger than they should. That results in North America looking larger than Africa, or China looking smaller than Greenland, when really the opposite is true.

Those criticisms aren't wrong, but they ignore that the original point of Mercator's projections were as a navigational tool for sailors. And, despite the map's shortcomings, it remains extremely handy for that purpose.

Other projections have come in and out of vogue, but all of them have issues. There are many variations of the Mercator projection that try to twist the formula, with varying success. Alternative solutions like the Robinson projection fix some issues, but are still distorted at the poles.

The Robinson Projection

The Robinson Projection (Wikimedia Commons)

The Gall-Peters projection, designed as a response to the Mercator projection's flaws, is also distorted near the poles.

Gall-Peters Projection

The Gall-Peters Projection (Wikimedia Commons)

Each map has its own advantages and compromises, like Mercator's.

The Mercator Projection

The Mercator Projection (Wikimedia Commons)

In an era of digital mapping, however, Mercator's work has reemerged thanks to its readability. Most sites and apps use the Web Mercator projection. Mercator never could have anticipated being part of an app on your phone, but he probably would have recognized his map.