Mapmaking - The Science of Navigation - page 91

sixth century BCE, was the first Greek who is said to have produced a map,
though it has not survived. The Chinese made maps for military purposes
and to help with water conservation. In the ninth century Al-Kwarizmi
created a world map based on that of Ptolemy, whose method he sys-
temized and whose errors he corrected. 3 This Persian mathematician pro-
vided the latitude and longitude of 2,402 localities, and the Islamic regions
of his map were, unsurprisingly, more accurately drawn than they were in
Ptolemy's map. Later in the same century Al-Biruni (whom we met in
chapter 2 measuring the earth) discussed map projection—in particular,
projecting a hemisphere onto a plane. He treated measurement errors
systematically; in this, too, he was ahead of his time.
The maps of medieval Europe were not intended as representational—
that is the kindest way of putting it. More than 1,100 medieval mappa
mundi (maps of the world) have survived, and they display orthodoxy
rather than geographical knowledge. Ptolemy had been translated into
Latin from Greek around 1400 CE and was accepted by the Church. The
teachings of other Greek philosophers were not, if they made statements
that contradicted the Bible. During this period, many of the European
world maps were of the T-O type, meaning that the land mass of the earth
was represented as circular (the O ), surrounded by water, and separated
into three continents by large rivers and seas that formed a T (fig. 4.2a).
Above the T was Asia; to the left of the vertical part of the T was Europe,
with Africa to the right. The waterways that formed the T were the Danube
and Nile Rivers and the Mediterranean Sea. Jerusalem was in the middle of
the circle (because the Bible referred to it as the center of all things). The
T-O maps were oriented with east at the top.
In parallel with the T-O world maps, there built up from the fourteenth
century smaller-scale maps of the Mediterranean and Black Sea regions
that were intended as practical guides for sailors. The representations of
coastlines in these maps were by far the most accurate to this date. These
maps were created and continuously revised by the many sailors who plied
these waters using the newly developed (for Europe) magnetic compass.
The practical nature of these portolan maps (the word comes from the
Italian for a sailing manual) can be appreciated from the fact that they
showed the predominant wind directions for the coastal regions portrayed.
3. We get our word algorithm from Al-Kwarizmi's name. Around 830 CE he wrote an
influential treatise on mathematics from which we derive our word algebra .