Is there a cartographic term for this?
March 1, 2010 12:25 PM   Subscribe

Is there a cartographic term for this?

On old nautical charts, there are often (bearing?) lines all over the place, which intersect to form a sort of star-shape. See this image please: Is there a name for the star-shaped convergence? Is their placement arbitrary? It looks arbitrary. Did the cartographer simply place them at intervals around a point of interest or a coastline, like numbers on a clock face?

Tried Google, tried Wikipedia, tried some cool cartographic luck.
posted by rahnefan to Travel & Transportation (9 answers total) 4 users marked this as a favorite
Response by poster: I'm not talking about a compass rose btw.
posted by rahnefan at 12:26 PM on March 1, 2010

Check out wikipedia's page on Portolan charts. It includes this statement:
The straight lines criss-crossing many portolan charts represent the thirty-two directions (or headings) of the mariner's compass from a given point. This is similar to the compass rose displayed on later maps and charts. Naming or demonstrating all thirty-two points is called boxing the compass.
posted by pappy at 12:30 PM on March 1, 2010

Portolan charts.
posted by carter at 12:42 PM on March 1, 2010

Oops. On preview ...
posted by carter at 12:42 PM on March 1, 2010

I'm also seeing in some references that the lines are referred to as "rhumb lines," which provided bearings to things on land for sailors to make reference to.
posted by pappy at 12:53 PM on March 1, 2010

Response by poster: But no name for where they intersect? I'm starting to think that it must be called a compass rose after all. It performs the same function as a compass rose. So were they placed arbitrarily or at specific latitudes/longitudes?
posted by rahnefan at 1:18 PM on March 1, 2010

Best answer: It has been argued (by, um, Prince Youssouf Kamal as quoted in Hapgood's Maps of the Ancient Sea Kings and quite possibly elsewhere) that these are construction lines used to help make accurate copies of the charts. As such, their location on any given chart is wherever they were on the one this one was copied from.

Blake, in The Sea Chart, refers to portolans as "wind rose directional charts with rhumb lines drawn to show these".

Neither of these sources appear to have any particular name for the star-shaped convergence points, although they do seem to be the origins of the wind roses which developed into compass roses.
posted by Lebannen at 1:43 PM on March 1, 2010 [3 favorites]

Response by poster: Wind rose. That makes sense, Lebannen. Thanks.
posted by rahnefan at 2:09 PM on March 1, 2010

(pappy: I think they are rhumb lines, but that just means that they're lines of constant heading. That in itself doesn't explain why there are a bunch of them on the map, though.)
posted by hattifattener at 7:45 PM on March 1, 2010

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