2017-06-27
Taprobana is Borneo
IMG Image
Ptolemy's mysterious island Taprobana is Borneo and it's quite
obvious. But since the current consensus written in stone is that
Taprobana was Sri Lanka, I'll spell it out with pictures.
(There is an in-depth essay on this by Dhani Irwanto
(Taprobana_is_not_Sri Lanka_nor_Sumatera,_but_Kalimantan) that I
found after drawing these maps, making this quite redundant. But
well.)
Long story short, Ptolemy drew nice maps of the known world in the
second century CE. The maps resurfaced in 1400, but since
cartography hadn't advanced virtually at all during the dark ages,
there was much confusion on where and what Ptolemy's Taprobana was.
Somewhere along the line it was agreed that Taprobana must be Sri
Lanka / Ceylon. Wrong!
IMG Ptolemy's map
This comparison is based on a 1535 edition of Cosmographia Claudii
Ptolomaei Alexandrini. In these comparisons Sri Lanka is first,
Taprobana in the middle, and Borneo on right.
Argument #1: Just Look at Them
IMG Shape comparison
If you were to describe the outlines of these maps, which one would
be "looks like a potato", and which ones "has a bay at northeast
and southwest, about three distinct capes"? (Borneo map is rotated
30° counterclockwise.)
To make this a bit more objective, I drew a convex hull around the
islands, extruded each edge of the polygon into a rectangle that
covers the whole concave part (ie. the bay), and then drew these
pieces end to end, starting from the northmost point, going
clockwise.About the same information on the right, as a spectrum of
'bayness'.
Note that in addition of the general profile, also the roughness
(deepness of bays) of Taprobana and Borneo correspond very well.
There certainly are a few features that make Sri Lanka a good
candidate, but compared to Taprobana I don't think there is much
question of who takes the cake.
IMG Profiles
IMG Profile 'spectra'
You could compare coastlines or any polygons this way by
cross-correlating the produced values. This feels so simple that
someone probably has written a paper on it, but I couldn't find
any.
IMG Position in respect of the equator
Ptolemy knew about latitudes. Would he have made a 7° mistake? Keep
in mind that determining the latitude is a simple matter of
measuring the angle between the horizon and the North Star, a task
every ancient mariner knew at that time.
Argument #3: Surroundings
IMG Surrounding islands
Sri Lanka is basically surrounded by non-volcanic sea floor, with
closest islands 230 km to the west and 1250 km to east. Borneo is
surrounded by islands, as is Ptolemy's Taprobana.
Argument #4: Mountains
IMG Mountains
Taprobana distinctly has a range of mountains going up to the very
top of the island, whereas Sri Lanka is somewhat flat with Central
Highlands and Adam's Peak in the southern half. Also notice
Taprobana's small spot of mountains at the southeast cape, exactly
the same as in Borneo.
Argument #5: Rivers
IMG Rivers
All five of Taprobana's rivers can be found among the largest
rivers of Borneo, except for the topmost one, which also can be
found among smaller rivers. The rivers of Borneo depicted here are
straight from Natural_Earth dataset to avoid cherry-picking.
Arguments #6 to #n:
As mentioned, Dhani Irwanto has examined this connection
extensively, and especially provides speculation on the
corresponding geographical names. The only one that was obvious to
me was Baracus Fluvius corresponding with modern Barito in the
southeast.