Originally, this device was used to indicate the directions of the winds (and it was then known as a wind rose), but the 32 points of the compass rose come from the directions of the eight major winds, the eight half-winds and the sixteen quarter-winds.
In the Middle Ages, the names of the winds were commonly known throughout the Mediterranean countries as tramontana (N), greco (NE), levante (E), siroco (SE), ostro (S), libeccio (SW), ponente (W) and maestro (NW). On portolan charts you can see the initials of these winds labeled around the edge as T, G, L, S, O, L, P, and M.
The 32 points are therefore simple bisections of the directions of the four winds (but the Chinese divided the compass into 12 major directions based on the signs of the Zodiac). For western apprentice seamen, one of the first things they had to know were the names of the points. Naming them all off perfectly was known as "boxing the compass."
The colors on the figure are supposedly the result of the need for graphic clarity rather than a mere cartographical whim. On a rolling ship at night by the light of a flickering lamp, these figures had to be clearly visible. Therefore the eight principle points of the compass are usually shown on the compass rose in black which stands out easily. Against this background, the points representing the half-winds are typically colored in blue or green and since the quarter-wind points are the smallest, they are usually colored red.
Reprinted with permission
- Cartographical Innovations: an International Handbook of Mapping Terms to 1900
- ed. by Helen M. Wallis and Arthur H. Robinson. - Tring, Herts: Map Collector Publications in association with International Cartographic Association, 1987. - ISBN 0-906430-04-6. (This was really quite good, and full of interesting history and details about maps - Bill)
- by David Greenhood. - The University of Chicago Press, 1964. ISBN 0-226-30696-8