11 November 2012

Portolan charts

The radiating lines on this portolan map of 1311 (found here) resemble the criss-cross lines of yarn wound onto a ball. I am interest in the geometry of the resulting net... its seeming randomness, depending on where the points are located. (Could you print with this ball of yarn??)
Intriguingly the intersections of the portolan lines also resemble those of the pacific-ocean stick charts.

The word "portolan" comes from Italian - "related to ports or harbours" - and the charts are based on compass directions and estimated distances observed by the pilots at sea. The charts of the Mediterranean and Black Seas were first made in Italy and Spain in the late 13th or early 14th century. During the Age of Discovery, when ships sailed along uncharted coasts to make lucrative trade discoveries, the charts were regarded as state secrets.

Thirty two lines - the mariner's compass - radiate from each point. The charts offered a realistic description of the shore and of useful harbours. They were most useful in smaller waters, rather than for crossing the ocean.

Here's another chart of the Mediterranean and Black Seas (1320-1350), from the Library of Congress website -
(North is at the bottom - the toe of the boot of Italy, near the centre, points upward.) In terms of mapping, it's all about the water's edge, getting from one harbour to another - an orientation we have lost as land travel became less difficult.

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