Long
before the magnetic compass, which was first used extensively by sailors in
the 13th century, the wind rose was used to orient travelers by elaborate drawings
on maps. The modern wind rose differs from the medieval wind rose in that it
describes not only the cardinal directions, but also the amount of wind blowing
from each direction. In this example, the 16 cardinal directions each
have a line of a specific length. The length of each line is determined by measuring
how often wind blows from that direction.
The large arrow coming from the center of this wind rose represents the general
direction in which wind blows. This arrow is created by averaging all the lines
together. Notice that in Alamosa, Colorado very little wind comes directly from
the north, while the majority of wind arrives from the southwest and flows to
the northeast (large arrow).