Rose wind

[Naima]

How to use rose winds in maps ? I mean where they shoudl be placed?

I for example have made a rose wind, its cool to see in correct angle but the map itself is tilted to better fit land in the rectangular shape and so the North is twisted in direction , should I twist also the wind rose? or not ? How is it used in maps , I noticed that some ancient maps have intricated webs of lines, are those used for something?

[Gaheris]

North on a compass rose should point toward North on the map rather than just "up". The only excuse I can think of (if you really want it pointing toward the top of the map) is that the fictional culture considers a direction other than North to be the most important (for instance East being more important in early-mid medieval maps), and that could conveniently be whatever direction the top of your map is in.

As far as I can guess, the lines on old maps (probably "charts" really, as the lines are usually only in the sea) are to make it easier to judge the directions between places not close to the compass rose. I hope that makes sense...

[Hai-Etlik]

The first and most important thing to understand is that not all maps should have a compass rose and many outright should not.

A compass rose is a functional part of a map just like a scale, graticule, legend, neatline, or the feature symbols themselves. A compass rose says that there is some system of measuring direction which, over the extent of the map is within a fairly fine tolerance of being bearing preserving. If this is not true of your map, it is outright WRONG to put a compass rose on it. Being bearing preserving means that if you measure a bearing against your system of direction in the reality of your world, then it should be the same bearing when measured on your map. If your world is a spheroid, then this means your map either has to be fairly large scale (covers a small area but draws it larger) in a projection appropriate to that extent, or it needs to be in a Mercator Projection aligned to your direction system. "Normal Mercator" is the aspect of the Mercator projection aligned to the planet's rotation.

For instance, this map is in a polar equidistant azimuthal projection. North is "toward the centre" and south is "away from the centre". It's meaningless to put a compass rose or even a north arrow on it.
Attachment 105896

This map is in Winkel Tripel. A projection appropriate for global reference maps like atlases or schoolroom wall maps. The north edge is "north" but the exact direction of north varies over the map.
Attachment 105895

This map is in plate carrée. This projection is mostly used for input into other processes. It's not very good for display. The cardinal directions are preserved, but "diagonal" directions end up as curves. If you really felt it was necessary, you could technically put a north arrow on this map, but a compass rose would be wrong
Attachment 105897

This is the Mercator projection. You could put a compass rose on this map, although it still isn't necessarily a good idea.
Attachment 105898

This is a large scale map in UTM 10 N. This is a Transverse Mercator projection with the Mercator projection wrapped around the meridians 123° E/W instead of the equator and taking just the bit 3° to either side of 123° W. This map covers 123° 30′ W to 123° 30′ W and 48° 15′ N to 48° 30′ N so it is inside that narrow 3° band and is very close to being bearing preserving. You could put a compass rose on it. This map has a north arrow with declination indicator instead which is typical of topographic maps.
Attachment 105902

This is a nautical chart in normal aspect Mercator. If you are at a very large scale like this, Mercator's distortions amount to just an additional scale factor which you can incorporate easily (this is the basis of zoomable web maps). Note that this is the first map that does have compass roses, three of them. Navigational charts for air and sea are the kind of map that really should have compass roses. Putting them on other maps is a bit of an affectation, sort of like putting a ship's wheel in a car in place of a steering wheel at best, and if the map is not bearing preserving it's more like putting a ship's wheel in a helicopter.


Now, there were probably some historical cars with sailing style wheels for control and for certain historical maps or maps mimicking them you can get away with compass roses, as long as they are bearing preserving. If it's not bearing preserving, you are in just plain wrong territory.

You can use another pair of antipodal points instead of the poles and you can orient your map however you want. All of that just rotates these factors around. If you want west to be up, sure. If you want your 0 direction to be "toward the temple of the navigation god" instead of "toward the point at which the surface is rotating counterclockwise" then that's fine, as long as you have an appropriate "compass".

Now, how you use a compass rose is important and it's good that you asked about it. The main thing a compass rose is used for is to align with parallel rulers.



You can use these to transfer a measured bearing from the rose to a point, or from a pair of points to the rose to measure. This requires being able to align an edge precisely with the rose to take the measurement. This is why a rose should have nice sharp straight lines, points, and/or crosses to line up on. You need the centre point (often crossed lines) and the point indicating the measure (a literal point of a star shape traditionally, a short radial line on modern roses.) If you cover up the centre with something, decorative so that there's no sharp centre point, you force the user to figure out the opposite point which isn't to hard on a low precision rose, but gets harder as the rose gets more detailed. Some of my maps do this but they are very much "cars with ships wheels" done intentionally and they are low precision.

The radiating lines are called "rhumb lines", "loxodromes", or "lines of constant bearing". They are just extensions of the compass rose. They are a convenience to reduce the distance you need to go with your parallel rulers. As the rulers got better and more precise bearings were needed, they were dropped. Like roses, they should only be used on maps that are bearing preserving and they are meant to be used on navigational charts. They will look out of place on a modern navigational chart though. Don't confuse them with graticules which are about location rather than direction. Rhumb lines look like webs of radiating lines that intersect in a sort of cat's cradle. Graticules are grids.

Rhumb Lines:
Attachment 29701

Graticule:
Attachment 43382

[Pixie]

Marvellous answer Hai! This text of yours should go to a sort of beginners guide to map making.
I'm glad you took some of your time to write it. Thanks.

... sent from mobile ...

[Mouse]

It reads very interestingly, but I can't see most of the attachments

[Naima]

Thankyou , I was planning to add a compass rose and eventually just other two minor ones to represent two moons , but not sureyet, I will tilt the Rose wind to represent the correct direction. I have added it to the map couse I am taking inspiration from an original Fresco where there is one , but I won't trace all intricate web lines then Thankyou .

[Arkidemis]

Thank you very much for the explanation. I too am having issues seeing the attachments however.