I was poking around some ancient maps for inspiration on style and I REALLY love aesthetic of these sun- compass-looking things in this map. They look like they have some function of triangulation and since this appears to be a fragment of a much larger map, I can only assume that the other lines belong to other sun-compasses, but I have no idea what they're really called.
Anyone know or have any guesses?
They are called Wind Roses, I think. The lines radiating from them are called Rhumb Lines.
Thank you very much! :D
but... I have to ask another question now... why are there so many?
Trying to utilize the internets, but I've stumbled upon no answers.
The rhumb line is a line of constant bearing across the earth's surface, and it is an aid to navigation that permits navigation without complex tools or detailed knowledge. The locations of the roses are rallying points, which can be used as starting positions or waypoints along your route. Leave port, sail in a straight line until you reach the rallying point, then turn and sail in a straight line until you reach the next, then turn and sail in a straight line to your destination port. You can thus connect almost any two ports on this map using only two waypoints, and you don't have to risk your ship on the shoals by coasting.
It's important to realize that rhumb lines usually aren't straight (on the globe), any that aren't in the four cardinal directions are spirals. The meridians and the equator are both rhumb lines are great circles ("Straight lines" in spherical geometry) The other parallels are all regular circles. Maps that show rhumb lines are either large scale, so they only show a short section of the spiral that doesn't show much curvature, or they are in the Mercator projection, which distorts things to make rhumb lines appear straight.
Rhumb lines and compass/wind roses are indications that the map is bearing preserving, and tools to aid in taking advantage of that property for navigation. Rhumb lines are mostly associated with "Dead Reckoning" navigation.
Rhumb lines are often drawn in a web of sorts, centring a cluster of lines at each vertex of a regular polygon so that the lines intersect the other verticies. The map you've linked to is doing this although you can only see a portion of the whole pattern. The whole thing looks like this:
@Midgardsormr & Hai-Etlik -- Thank you so much for your answers. This explains a lot and is absolutely fascinating/beautiful!
Would wind-roses function the same way over large areas of land?
Theoretically yes, but dead reckoning navigation is a lot harder over land since the terrain rarely cooperates, even in grasslands. Not to mention those obnoxious farmers and their fences. It's usually much easier and faster to just follow the roads.
Sometimes you'll run across an overland map with rhumb lines, but in most of those cases, it's probably because the cartographer didn't actually know what the lines were for and thought they were merely a decorative device. I've even seen one example where someone added false (and incorrect) rhumb lines to an original Mercator.
I figured as much. They are REALLY NICE looking from an artistic standpoint but I can't imagine how absurdly idiotic they look when used incorrectly. :P