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Broad Reach

Off course: 500 years of flawed maps

June 7, 2012 by robert in Broad Reach, Featured with 0 Comments

Place an upright paper cylinder over a globe. Shine a light from inside the globe and you’ll project every point on that globe’s surface onto the inside of the cylinder. Now open that cylinder and lay it flat on a table. Voila! A world map! Hey, wait a minute! On your map Greenland is 17 times bigger than Africa!

When Gerard de Cremer did this trick in the 17th century he was stumped by the problem of how to accurately display on a flat surface the image from a round globe. He never resolved that. This year marks the 500th birthday of the man better known as Mercator whose groundbreaking cartographic work still serves navigators today. If he were alive today, Mercator  would be pleased to see that making an accurate flat map cannot be done. In the past 5 centuries, many smart people have gone to the drawing board, armed with bewildering mathematical formulas. They have produced a slew of projection methods _ from equirectangular to pseudoconical, from polyhedral to quincuncial _ that yielded wildly different world maps. These have only one thing in common: all are incorrect.

With cars, planes, rucksacks and boats these days packed with satellite navigation gear, Mercator is not on many lips anymore. Still, his cartography triggered a key insight in global navigation: that the most direct route on the ocean is not a straight course, but a rhumb line which crosses all longitudes at the same angle.

Mercator (1512 –1594) was born in Rupelmonde, Belgium. Educated in Den Bosch (Netherlands) and the University of Leuven (Belgium), he initially made mathematical instruments and became a highly skilled engraver of brass plates. His cartography began when he drew a map of Palestine (1537), followed by one of the world (1538) and Flanders (1540). In 1544 he was charged with heresy for embracing Protestant beliefs and spent seven months in prison before the charges were dropped. In 1552, he moved to Duisburg where he opened a cartographic workshop and became the leading European globe maker of his age. In all, 22 pairs of his globes _ each consisting of a terrestrial globe and a matching celestial globe _ have survived.

But very few people stare at globes anymore. And what a pity that is! What is lost when we lose sight of globes? “An accurate sense of home,” according to Mark Vanhoenacker, a writer and airline pilot based in New York. “The view of a Roman street on Google Maps is wonderful,” he wrote in The New York Times in 2012. “But only after a globe has shown you Italy. And no online or paper map has yet succeeded in stretching a round planet onto a flat surface … Only a globe is both simple and right. Simple because it’s right.” 

Put another way: Nothing shows the imperfection of flat maps better than globes. 

The ‘Mercator projection’ shows the world’s parallels and meridians as straight lines. This means his projection cannot show 2 poles. Map makers since Mercator have all had to ignore some key measuring properties _ such as area, shape, direction and distance or scale _ depending on what they wanted to show. A political map of the world looks very different from one showing the right relative sizes of the continents, or the distribution of trade or religions.

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