The Compass Rose - Map of China: Decoding the Secrets of a Vanished Cartographer - page 106

andeightofthestemsbutalltwelvebranches.Thatmixmeansmasteringalexicon
of twenty-four names in fixed sequence without an internal logic that I've been
abletodiscover.Aftermasteringthetwenty-fournames,thingsgeteasier.Thenext
trisection produces a total of seventy-two compass points. Rather than give the ad-
ditional forty-eight points forty-eight new names, the Chinese system gives them
names based on which two of the twenty-four they are between.
This part of the system is completely regular and easily understood. Let me
demonstratehowthisworksbygivinganexample.Ifyouaresailingduenorth,you
are travelling in the zi direction at 0°. Turn 15° east and you are on a gui course.
Vary your zi course by 5° to the east and you are said to be sailing guizi , meaning
to the gui side of zi . English nautical convention would say that you are going ' zi
by gui '. (Think of Alfred Hitchcock's North by Northwest - although, as has often
been pointed out, there is no such direction; the correct bearing is 'north by west'.)
Shift another 5° to the east, and you will be travelling zigui , or ' gui by zi '. That
is, you will be on the zi side of gui , or 5° west from gui at 15° - which is to say,
10°. Turn another 5° to 15°, and you are on a straight gui direction. Keep moving
around the compass by 5° increments and the pattern repeats itself with the next
pair of names. If none of this makes obvious sense, it doesn't require mastering.
Readers keenly interested in how the system works will find it laid out in the first
appendix. ***
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I observed at the start of this chapter that the most important thing to know about
the compass rose on the Selden map is that it shouldn't be there: roses did not be-
come part of Chinese cartographic practice until the twentieth century. Hyde re-
gisters no surprise at seeing it there, but then why should he, as he had few other
Chinese maps against which to compare this Chinese map? He would have known
them from European maps, of course, and yet as it happens, compass roses were
disappearingfromEuropeanmaps.BythetimeHydeandShenwereannotatingthe
Selden map, the compass rose had become a hold-over from a particular phase of
European mapping known as the portolan chart.
Portolan charts were charts of the places documented in the old portolanos or
rutters.Theearliestsurvivingexampledatesfromthethirteenthcentury.Theycon-
tinued to be used until the seventeenth, when mathematical cartography pushed
aside the method on which they were drawn. Rather than mapping a route on the
water, portolan charts mapped the coastlines along which sea routes ran. The chal-