Heaven is Round, Earth is Square - Map of China: Decoding the Secrets of a Vanished Cartographer - page 141

required stretching the globe towards each pole, increasing the degree of stretch at
the rate of pi as he approached each pole. This north-south elongation entailed a
proportionate east-west stretch that also increased the further one moved from the
equator. Bend the model around on itself, and the earth became in effect a cylin-
der. Mercator got to his model through empirical experimentation but was suffi-
cientlywelltrainedinmathematicstodetectitsgeometricregularity.Thedistortion
he needed in order to ensure that sailing routes appeared as straight lines was not
random but could be worked out by precise calculation. The result is what we now
call the Mercator projection.
The appeal of the Mercator projection was that it worked for navigators, and in
the sixteenth century they were the ones sailing across vast spaces and needing re-
liable maps. Mercator simplified the challenge of plotting a course by drawing the
world in such a way that any point A and point B could be connected by a straight
line that stayed on a single compass bearing. The actual course the ship followed
was in reality curved and therefore not the shortest distance between two points,
but it could be calculated simply and reliably by by locking a ship's bearing on a
fixedcompassdirection.Thedisadvantageoftakingaslightlylongerroutewasoff-
setbythecertaintythatyouwouldarriveatyourdestination.Mercatorhadsquared
Zhang Huang's circle.
Mercator tried to put his projection into popular circulation with his massive
world map of 1569. It didn't take immediately, but by the end of the century it
had become standard. Even today Mercator's redrawing of the world is the image
most of us carry around in our heads: Canada, Greenland and Russia inflated bey-
ond their actual sizes, and Antarctica distorted into a titanic continent, like Atlas's
shoulders, on which the world rests. Other cartographers have tinkered with Mer-
cator's model, trying to adjust it to reduce distortion without sacrificing accuracy.
Mercator's colleague Abraham Ortelius came up with a method that curved Mer-
cator's lines of longitude on either side of the prime meridian (the central line of
longitude onamap), increasing the degree ofcurve the further hewent. The result,
called the pseudo-cylindrical projection, was a compromise between square and
round that reduced the distortion caused by the Mercator projection. This was the
projection that Matteo Ricci used for the mappa mundi he drew for Chinese view-
ers, and which Zhang Huang reprinted in his Documentarium (Fig. 24). Copies of
copies of copies: this is how cartographic knowledge spreads.
For his regional maps, including that of China, Ortelius tried yet other projec-
tions.Hisdatawereothers'renderingsofChinaandthereforetooimprecisetoper-