Compass Rose and Lines: How do they 'work'?
This is ore of a generic mapping question rather than using CC3; I want to know the 'logic' behind compass roses and the navigation lines coming off their 32 points. I've done a little research, but it's not really winking in.
My specific need is to know where the compass roses should be placed and if the lines coming off them mean something, if the intersections mean something, and how the resulting 'web' of lines are actually interpreted and used?
I want to add compass roses and lines to some of my maps, but I don't want to throw them down randomly, I want to follow the logic behind them.
My specific need is to know where the compass roses should be placed and if the lines coming off them mean something, if the intersections mean something, and how the resulting 'web' of lines are actually interpreted and used?
I want to add compass roses and lines to some of my maps, but I don't want to throw them down randomly, I want to follow the logic behind them.
Comments
I usually just go by historical examples and try to match them in spirit instead of exact technique. Here is an example: http://historicurbanplans.com/dbimages/products/123783668674129.jpg
Generally speaking, a compass rose is an aid for aligning a map with the true compass points. By convention, 15th century and older European maps are usually drawn with north at the top of the page, meaning that many maps don't need (or have) a true compass rose because they are already aligned with the main compass points. When maps are drawn for a specific purpose and the page centerlines don't align with the cardinal points, then a compass rose is pretty much mandatory for situating the map in context.
16th century (or thereabouts) oceanic navigation maps tend to have groups of lines that radiate from the 8 main directions around the edge of a map. These lines provide a convenient framework for navigating a straight line between two ports. Pick a one of these rhumb line marked on the map and follow it, keeping the compass heading constant and you'll eventually get about there the map shows. Note that these maps are always in the Mercator projection, a projection where a straight line on the map translates to a constant bearing with a compass. These navigational aids seem to have become somewhat less popular as time wore on, though. If your map isn't an oceanic navigation map, then the fancy web of lines will be somewhat out of place.
This will - ultimately - be a naval map, thus the compass roses seemed relevant and a good touch.
Like you Ralf, I have tended to follow the 'spirit' of them in the past, but after reading that they actually had a purpos, I didn't want to blatantly fly in the face of that and do something heinously wrong!
jslayton, thank you, you reaffirmed something I read, but also - I think - clarified their usage. I had been getting hung up on the destination lines going somewhere and the original placement of the compasses - or indeed the intersections - meaning something, and - after studying old maps - I just oculd not find a pattern in them at all.
However, it sounds like the lines are less a path ... or 'road' ... to a direct point, but rather the direction to sail and - if you did - the point where you will end up, regardless of where that point is.
So, if you want to sail 2,000 miles across the ocean, pick the direction on the nearest compass rose, then follow it and you will end up at x-point on the opposite coastline; it may not be an actual port or even geographic feature, but you'll know where you are at the other end and can sail from there.
Sounds like dropping in compass roses near typical sailing-from points would make sense, therefore - yes?
I have seen pictures of old map blanks that have just these lines, a border, and a space for a label. The ship's navigator would then draw on this blank chart at an appropriate scale.
http://butronmaker.blogspot.com/ shows some examples of portolan charts that have the navigation lines at major ports, which sounds like what you want to do.