Mercator – Surveyor and Mapper

"Let none dare to attribute the shame
Of misuse of projections to Mercator’s name;
But smother quite, and let infamy light
Upon those who do misuse, publish or recite."

  [Author unknown]

Take a sphere (or spheroid) and drop it into a hollow cylinder of equal (or onto one of smaller) diameter; project the surface of the sphere upon the surface of the cylinder; cut the cylinder open and flatten it out. Call the resulting map a "Mercator Projection" as it has been for more than 400 years, because that is how Gerardus Mercator in 1569 produced his famous map? – He did nothing of the sort.

Not that Mercator does not deserve to be honored for innovations in mapping, his place in the history of cartography is assured even without erroneously attaching his name to latter day projections all the way down to the Transverse Mercator grid of our State Plane Coordinate System. He is rightfully considered one of the greatest mapmakers of all time, devoting his entire life to the betterment of maps.

Mercator, the sixth child of German parents, was born Gerhard Kramer on March 5, 1512 in the town of Rupelmonde in Flanders. Orphaned at an early age he grew up under the tutelage of a relative. In 1530 he entered the university of Louvain (today Leuven in Belgium), in the process and in keeping with the custom of the time, latinizing his name to Gerardus Mercator. There he studied mathematics, geometry, geography and engraving, and upon graduating set up shop as a surveyor, instrument maker, and producer of globes and maps. This was the age of the great voyages, the world was expanding, sailors and travelers were clamoring for accurate maps, Flanders was prosperous, and Mercator’s shop flourished. 

It was also a time of religious bigotry, rulers not taking it kindly when surveyors and mapmakers dared to change the sacrosanct view of the universe. For a map of Flanders Mercator spend three years of his own surveying, an activity that was viewed by the authorities with great suspicion. A Protestant in a Catholic province, he was imprisoned in 1544 and charged with of heresy. Influential friends obtained his release but he thought it wise not to push his luck and to remove himself with his business to the adjacent and more tolerant German Duchy of Cleves, where in 1552 he settled permanently in the city of Duisburg. In 1559 he was appointed cosmographer to the court of the Duke.

The continuously growing volume of new geographical data persuaded Mercator to abandon the time-honored theories of Ptolemy and other predecessors, and to construct his maps and globes to reflect the latest observations and geographic knowledge. As the areas to be mapped grew in size, so did the errors associated with the representation of a curved surface on a flat chart. This was felt especially painfully by mariners who since times immemorial had only followed coast-lines (where mapping errors didn’t matter much) but now were crossing the immense expanse of the oceans.

The university-educated Mercator sought a solution in mathematical formulae and by the late 1560’s constructed a grid of meridians and parallels which for the first time showed the converging meridians as parallel and equally spaced straight lines, extending vertically from top to bottom of the map. To compensate for the east-west error that grows with latitude, Mercator spaced the parallels in a corresponding ratio, drawing them increasingly further apart as they approach the pole. It is important to note that this can only be done by mathematical analysis and NOT by projection, so in a sense the "Mercator Projection" is no projection at all.

It is only fair to point out that Mercator’s solution was approximate, neither the knowledge of the true size and shape of the globe nor the mathematical resources of his time (calculus had not yet been invented) being adequate to permit great accuracy. It is also readily apparent that the large distortion of area, especially in the higher latitudes, makes that kind of a map unsuitable for land use. But Mercator intended his map to be used for navigation at sea and as such it was an instant success. On the new nautical chart navigators could now plot a ships course of constant compass direction (loxodrome) as a straight line, the only "projection" where such is the case. A loxodrome is not however the shortest distance between two points because it is not a great circle arc.

Mercator published his revolutionary new map in 1669 under the title: "A new Arrangement of the Meridians with Reference to the Parallels." It is the prototype of the modern marine chart and made him famous.

Mercator devoted the last years of his life to produce a series of detailed maps of various portions of Europe. When it was published a year after his death (he died in Duisburg on December 2, 1594) it showed on the cover a picture borrowed from Greek mythology: Atlas, brother of Prometheus, holding the world on his shoulders. It gave us the name "Atlas" for any collection of maps.