SCIENCE ARCHIVES: MERCATOR
You know the map, and you probably know it distorts Greenland. What’s next?
Maps of the 1500s were badly designed. To seafarers, maps caused long detours, and even shipwreck. But with a new, brilliant method, cartographer Mercator converted the circular world into a rectangular map.
In 1543, Polish astronomer Nicolaus Copernicus publishes his book “On the Revolutions of the Heavenly Spheres”, which once and for all determines that our world is circular. But only 26 years later, cartographer Gerardus Marcator makes Earth flat again.
Mercator was born in 1512 in the city of Rupelmonde in what is now the Flemish part of Belgium. His family was wealthy, and Mercator was educated at the reputable University of Leuven, but fell into disgrace in the conservative, academic world. The young student had difficulties making the Catholic Church’s traditional world view tally with the discoveries, realizations, and results published by modern scientists in the early 1500s. He had to give up his dream of a university career.
Instead, the handy Fleming set out to work with the modern printing method of chalcography: a subject is engraved into a copper plate, which can subsequently be used to print the subject on paper. He also used his talent for precision work to build scientific instruments, and in 1535, he and famous mathematician, cartographer, and instrument maker Gemma Frisius made a star globe. Mercator’s contribution was to engrave the heavenly bodies into the copper ball, but the work probably made him interested in cartography.
In the following years, chalcography was still Mercator’s main line of work, but he also started to make geographical maps himself. Back in those days, most cartographers made their maps based on the recordings of other people, and the way in which Earth’s rounded stretches were depicted had been the same for centuries.
Roman maps remained the best
The cartography of the 1500s was based on the work that Roman mathematician, astronomer, and geographer Claudius Ptolemy carried out 1,400 years earlier.
Ptolemy knew that Earth is circular, but he did not go exploring himself, and – like other Roman citizens – he almost only knew the world surrounding the Mediterranean. Around 150 AD, he authored the work “Geographia”, in which he for the first time divided Earth into degrees of longitude
and latitude. In the book, he locates the positions of a series of places in a system of coordinates and, moreover, indicates several methods for depicting the circular Earth in a flat map. From a modern point of view, the maps are highly distorted, but that had more to do with Ptolemy’s lack of knowledge about Earth's dimensions land masses than with his cartographic method.
For centuries, cartographers used Ptolemy’s maps, improving them with new dis cover i es and more accurate measurements. But the world’s collection of maps was still based on his projection methods.
Luther jailed Mercator
However, Mercator believed that it was time for fundamental religious and cartographic changes. The former made him join Luther’s Protestant movement, which in 1544 earned him a heresy sentence.
After seven months in jail, he was released, and a few years later, he moved to Duisburg in what is now Germany – probably to avoid more religious prosecution, settling down as a successful cartographer. Gerardus Mercator produced a series of new, accurate maps and soon began to teach at the local university. In 1569, he was named a royal cartographer by the powerful William, Duke of JülichCleves-Berg. As Mercator was drawing up his maps, adventurous seafarers reached ever more remote corners of the world, bringing back not only exotic goods, rather new knowledge about Earth's geography. Nautical charts were still based on Claudius Ptolemy's ancient methods, and Mercator aimed to give seafarers a whole new world map which was easier to navigate by.
A rectangular world
Ever since Antiquity, cartographers had divided Earth into east-westbound parallels of latitude and north-southbound parallels of longitude. The distance between the parallels of latitude is the same from Equator to the poles, whereas the parallels of longitude meet by the poles, spreading out towards the Equator and meeting by the opposite pole.
When cartographers drew up 2D maps, they always depicted parallels of latitude and longitude as curves, and on those maps, it was difficult for navigators to set out a course. So, Mercator aimed to invent a map projection, in which parallels of both latitude and longitude are straight lines, and which distorts the shapes of the land masses as little as possible. On such a map, navigators would easily be able to indicate a compass course using a ruler.
In 1569, Mercator’s cartographic workshop introduced the revolutionizing world map “Nova et aucta orbis terrae descriptio ad usum navigantium emendate accomodata” – a new and more complete representation of the terrestrial globe properly adapted for use in navigation.
Complex mathematics
Nobody knows how Mercator worked out his map projection.
The underlying maths is complex, but the idea is simple: First, the distance between the parallels of longitude is stretched, so they no longer meet by the poles, but become parallel lines with the same distance between them.
This means that land masses, lakes, and oceans become wider – the further away from the Equator, the more they must be stretched to make the parallels of longitude parallel. To counteract the distortion of the real shape, the distance between the parallels of latitude are subsequently increased correspondingly. The further away from the Equator, the more the distance has to be stretched.
The result is a world map, in which the land masses do not have the correct area in relation to each other, but where compass directions are always straight lines. So, Mercator had turned the circular world into a flat rectangle.
New clock made map popular
The brilliant map ought to have been the dream of any navigator, but Mercator was too far ahead of his time.
Seafarers were conservative , superstitious people. They were used to navigating by the stars using primitive navigation instruments such as the astrolabe – the predecessor of the sextant. Nobody dared to navigate the oceans based on a map drawn up by a university professor, who had never been to sea himself.
Moreover, seafarers had no method for determining the degree of longitude, and without this information, Mercator’s map functioned just as poorly as any other nautical map.
Mercator proposed the use of portable clocks for the calculation of degrees of longitude, but the clocks of the 1500s were not sufficiently accurate. Not until 150 years later, when British clock-maker John Harrison invented a very accurate and robust nautical clock, could navigators determine their exact positions.
The invention made Mercator’s map projection very popular. Famous explorer James Cook used Harrison’s clock and
Mercator’s maps during his three major scientific sea voyages, and even today, the almost 500-year-old projection method is the most widely used for nautical maps.
Map collection was first atlas
After the publication of the revolutionizing world map, Mercantor devoted himself to a huge project. He aimed to include knowledge about the creation of the world, history, geography, and politics in one large work, and he set out on the huge task by making the copper plates that were to be used for the printing of the work’s maps.
In 1585, he published the first maps, and four years later another series, and in 1595, the “Atlas Cosmographicae” map collection was published. So, Mercator was the first to name a map collection an atlas. Unfortunately, Mercator never saw the atlas himself. The work with the maps had been strenuous, and he was an old man. He died in December 1594 at the age of 82, and his son, Rumold, published the “Atlas Cosmographicae”. The atlas was republished numerous times after Mercator’s death, and today, he is remembered as one of the greatest masters of cartography.