Compass rose


A compass rose, sometimes called a windrose or rose of the winds, is a figure on a compass, map, nautical chart, or monument used to display the orientation of the cardinal directions and their intermediate points. It is also the term for the graduated markings found on the traditional magnetic compass. Today, a form of compass rose is found on, or featured in, almost all navigation systems, including nautical charts, non-directional beacons, VHF omnidirectional range systems, global-positioning systems, and similar equipment.
The modern compass rose has eight principal winds. Listed clockwise, these are:
Compass pointAbbr.HeadingTraditional wind
NorthN0°Tramontana
North-EastNE45° Greco or Grecale
EastE90° Levante
South-EastSE135° Scirocco
SouthS180° Ostro or Mezzogiorno
South-WestSW225° Libeccio or Garbino
WestW270° Ponente
North-WestNW315° Maestro or Mistral

Although modern compasses use the names of the eight principal directions, older compasses use the traditional Italianate wind names of Medieval origin
4-point compass roses use only the four "basic winds" or "cardinal directions", with angles of difference at 90°.
8-point compass roses use the eight principal winds—that is, the four cardinal directions plus the four "intercardinal" or "ordinal directions", at angles of difference of 45°.
12-point compass roses, with markings 30° apart, are often painted on airport ramps to assist with the adjustment of aircraft magnetic compass compensators.
16-point compass roses are constructed by bisecting the angles of the principal winds to come up with intermediate compass points, known as half-winds, at angles of difference of 22°. The names of the half-winds are simply combinations of the principal winds to either side, principal then ordinal. E.g. North-northeast, East-northeast, etc.
32-point compass roses are constructed by bisecting these angles, and coming up with quarter-winds at 11° angles of difference. Quarter-wind names are constructed with the names "X by Y", which can be read as "one quarter wind from X toward Y", where X is one of the eight principal winds and Y is one of the two adjacent cardinal directions. For example, North-by-east is one quarter wind from North towards East, Northeast-by-north is one quarter wind from Northeast toward North. Naming all 32 points on the rose is called "boxing the compass".
The 32-point rose has the uncomfortable number of 11° between points, but is easily found by halving divisions and may have been easier for those not using a 360° circle. Using gradians, of which there are 400 in a circle, the sixteen-point rose will have twenty-five gradians per point.

History

Linguistic anthropological studies have shown that most human communities have four points of cardinal direction. The names given to these directions are usually derived from either locally-specific geographic features or from celestial bodies or from atmospheric features. Most mobile populations tend to adopt sunrise and sunset for East and West and the direction from where different winds blow to denote North and South.

Classical compass rose

The ancient Greeks originally maintained distinct and separate systems of points and winds. The four Greek cardinal points were based on celestial bodies and used for orientation. The four Greek winds were confined to meteorology. Nonetheless, both systems were gradually conflated, and wind names came eventually to denote cardinal directions as well.
In his meteorological studies, Aristotle identified ten distinct winds: two north-south winds and four sets of east-west winds blowing from different latitudes—the Arctic circle, the summer solstice horizon, the equinox and the winter solstice. However, Aristotle's system was asymmetric. To restore balance, Timosthenes of Rhodes added two more winds to produce the classical 12-wind rose, and began using the winds to denote geographical direction in navigation. Eratosthenes deducted two winds from Aristotle's system, to produce the classical 8-wind rose.
The Romans adopted the Greek 12-wind system, and replaced its names with Latin equivalents, e.g. Septentrio, Subsolanus, Auster, Favonius, etc. Uniquely, Vitruvius came up with a 24-wind rose.
According to the chronicler Einhard, the Frankish king Charlemagne himself came up with his own names for the classical 12 winds. He named the four cardinal winds on the roots Nord, Ost, Sund and Vuest. Intermediate winds were constructed as simple compound names of these four. These Carolingian names are the source of the modern compass point names found in nearly all modern west European languages.
The following table gives a rough equivalence of the classical 12-wind rose with the modern compass directions.

WindGreekRomanFrankish
NAparctias SeptentrioNordroni
NNEMeses or
Boreas 		AquiloNordostroni
NECaicias CaeciasOstnordroni
EApeliotes SubsolanusOstroni
SEEurus VulturnusOstsundroni
SSEEuronotus EuronotusSundostroni
SNotos AusterSundroni
SSWLibonotos Libonotus
or Austroafricus		Sundvuestroni
SWLips AfricusVuestsundroni
WZephyrus FavoniusVuestroni
NWArgestes CorusVuestnordroni
NNWThrascias Thrascias or CirciusNordvuestroni

Sidereal compass rose

The "sidereal" compass rose demarcates the compass points by the position of stars in the night sky, rather than winds. Arab navigators in the Red Sea and the Indian Ocean, who depended on celestial navigation, were using a 32-point sidereal compass rose before the end of the 10th century. In the northern hemisphere, the steady Pole Star was used for the N-S axis; the less-steady Southern Cross had to do for the southern hemisphere, as the southern pole star, Sigma Octantis, is too dim to be easily seen from Earth with the naked eye. The other thirty points on the sidereal rose were determined by the rising and setting positions of fifteen bright stars. Reading from North to South, in their rising and setting positions, these are:
PointStar
NPolaris
NbE"the Guards"
NNEAlpha Ursa Major
NEbNAlpha Cassiopeiae
NECapella
NEbEVega
ENEArcturus
EbNthe Pleiades
EAltair
EbSOrion's belt
ESESirius
SEbEBeta Scorpionis
SEAntares
SEbSAlpha Centauri
SSECanopus
SbEAchernar
SSouthern Cross

The western half of the rose would be the same stars in their setting position. The true position of these stars is only approximate to their theoretical equidistant rhumbs on the sidereal compass. Stars with the same declination formed a "linear constellation" or kavenga to provide direction as the night progressed.
A similar sidereal compass was used by Polynesian and Micronesian navigators in the Pacific Ocean, although different stars were used in a number of cases, clustering around the East-West axis.

Mariner's compass rose

In Europe, the Classical 12-wind system continued to be taught in academic settings during the Medieval era, but seafarers in the Mediterranean came up with their own distinct 8-wind system. The mariners used names derived from the Mediterranean lingua franca—the Italian-tinged patois among Medieval sailors, composed principally of Ligurian, mixed with Venetian, Sicilian, Provençal, Catalan, Greek and Arabic terms from around the Mediterranean basin.
The exact origin of the mariner's eight-wind rose is obscure. Only two of its point names have Classical etymologies, the rest of the names seem to be autonomously derived. Two Arabic words stand out: Scirocco from al-Sharq and the variant Garbino, from al-Gharb. This suggests the mariner's rose was probably acquired by southern Italian seafarers not from their classical Roman ancestors, but rather from Norman Sicily in the 11th to 12th centuries. The coasts of the Maghreb and Mashriq are SW and SE of Sicily respectively; the Greco, reflects the position of Byzantine-held Calabria-Apulia to the northeast of Arab Sicily, while the Maestro is a reference to the Mistral wind that blows from the southern French coast towards northwest Sicily.
The 32-point compass used for navigation in the Mediterranean by the 14th century, had increments of 11° between points. Only the eight principal winds were given special names. The eight half-winds just combined the names of the two principal winds, e.g. Greco-Tramontana for NNE, Greco-Levante for ENE, and so on. Quarter-winds were more cumbersomely phrased, with the closest principal wind named first and the next-closest principal wind second, e.g. "Quarto di Tramontana verso Greco", and "Quarto di Greco verso Tramontana". Boxing the compass was expected of all Medieval mariners.

Depiction on nautical charts

In the earliest medieval portolan charts of the 14th century, compass roses were depicted as mere collections of color-coded compass rhumb lines: black for the eight main winds, green for the eight half-winds and red for the sixteen quarter-winds. The average portolan chart had sixteen such roses, spaced out equally around the circumference of a large implicit circle.
The cartographer Cresques Abraham of Majorca, in his Catalan Atlas of 1375, was the first to draw an ornate compass rose on a map. By the end of the 15th century, Portuguese cartographers began drawing multiple ornate compass roses throughout the chart, one upon each of the sixteen circumference roses.
The points on a compass rose were frequently labeled by the initial letters of the mariner's principal winds. However, from the outset, the custom also began to distinguish the north from the other points by a specific visual marker. Medieval Italian cartographers typically used a simple arrowhead or circumflex-hatted T to designate the north, while the Majorcan cartographic school typically used a stylized Pole Star for its north mark. The use of the fleur-de-lis as north mark was introduced by Pedro Reinel, and quickly became customary in compass roses. Old compass roses also often used a Christian cross at Levante, indicating the direction of Jerusalem from the point of view of the Mediterranean sea.
The twelve Classical winds were also sometimes depicted on portolan charts, albeit not on a compass rose, but rather separately on small disks or coins on the edges of the map.
The compass rose was also depicted on traverse boards used on board ships to record headings sailed at set time intervals.

Modern depictions

The contemporary compass rose appears as two rings, one smaller and set inside the other. The outside ring denotes true cardinal directions while the smaller inside ring denotes magnetic cardinal directions. True north refers to the geographical location of the north pole while magnetic north refers to the direction towards which the north pole of a magnetic object will point. The angular difference between true and magnetic north is called variation, which varies depending on location. The angular difference between magnetic heading and compass heading is called deviation which varies by vessel and its heading. North arrows are often included in contemporary maps as part of the map layout.

Use as symbol