Secrets of the Selden Map - Map of China: Decoding the Secrets of a Vanished Cartographer - page 154

the Selden map makes this quickly apparent. Over all, the map has been drawn to
a scale of about 1:4,750,000. This is roughly the scale on which Borneo, Sumatra
and much of China are drawn. But the scale, it turns out, is not uniform across the
map. When you compare the Selden map with the modern conic projection, you
can see that some parts are too large and some too small. Measurement bears this
out.ThePhilippines andthenorthernpartofChinaalongtheGreatWallhavebeen
drawn on a scale that is double the scale of the rest of the map, about 1:2,400,000.
Thismeansthattheseareasaretwicethesizetheyshouldbeiftheyhadbeenprop-
erlyscaledtoBorneoortherestofChina.Therearealsoareasdistortedintheother
direction. In particular, mainland South-East Asia gets abbreviated. In Yunnan the
scaleshrinksto1:6,000,000,andinVietnamitdiminishestolessthan1:7,000,000.
What does this tell us? Does it argue against the idea that our cartographer used
a European map as his template to piece together the parts of East Asia? Possibly,
but I don't think this is the most interesting conclusion we can derive from the
variability of scale. To me it suggests that he was working from another data set.
The secret of his data came into view only when the team of conservators - Robert
Minte and Marinita Stiglitz of the Bodleian Library and Keisuke Sugiyama of the
British Museum - removed the cotton lining to which conservators in an earlier
century had glued and varnished it. By 2010 the map was in a sorry state, but the
team was able to lift the paper sheet on which the map was drawn without sacri-
ficing any of the original. Once the original had been cleaned and dried, they dis-
covered tell-tale marks on the back: drafts of the scale and rectangle at the top of
the map, plus signs that no one can decipher. Far more exciting was the discovery
of a series of connected straight-edge lines. When the conservators turned the map
backovertocomparethesewithlinesonthefront,theyfoundaperfectmatch.The
lines on the back exactly replicated the lines that form the main trunk route drawn
down the east coast of China on the front. How would this have come about? The
obvious explanation is that the cartographer started to draw his map on one side of
thepaper,thenturnedthesheetoverandredrewitontheother.Maybehewasprac-
tising; maybe he realised he had made a mistake. Whatever his reason, he wanted
to start again. The important thing here is not that he practised or made a mistake.
What the verso lines reveal is the key to his mapmaking method: he drew the sea
routes first. Rather than doing as we naturally would, outlining the coasts and then
filling in the routes to run between the ports, he drew the route lines first, based on
the route data in his rutters, and then filled in the coasts around them. So this map
is really not a map at all. It is a chart of sea routes. The landforms are approximate
afterthoughts.