Points of the compass

16-point compass rose

The points of the compass mark the divisions on a compass, which is primarily divided into four points: north, south, east, and west. These cardinal directions are further subdivided by the addition of the four intercardinal (or ordinal) directions—northeast (NE), southeast (SE), southwest (SW), and northwest (NW)—to indicate the eight principal winds. In meteorological usage, further intermediate points between cardinal and ordinal points, such as north-northeast (NNE) are added to give the 16 points of a compass rose.[1]

32-point compass rose

At the most complete division are the full thirty-two points of the mariner's compass,[2] which adds points such as north by east (NbE) between north and north-northeast, and northeast by north (NEbN) between north-northeast and northeast. A compass point allows reference to a specific course (or azimuth) in a colloquial fashion, without having to compute or remember degrees.

The European nautical tradition retained the term "one point" to describe ​1⁄32 of a circle in such phrases as "two points to starboard". By the middle of the 18th century, the 32-point system was extended with half- and quarter-points to allow 128 directions to be differentiated.[3]

Compass points

The names of the compass point directions follow these rules:

8-wind compass rose

  • The four cardinal directions are north (N), east (E), south (S), west (W), at 90° angles on the compass rose.
  • The four ordinal (or intercardinal) directions are formed by bisecting the angle of the cardinal winds: northeast (NE), southeast (SE), southwest (SW) and northwest (NW). The name of each ordinal is simply a combination of the cardinals that it bisects.
  • The eight principal winds (or main winds) are the four cardinals and four ordinals considered together, that is: N, NE, E, SE, S, SW, W, NW. Each principal wind is 45° from its two neighbours. The principal winds form the basic 8-wind compass rose.

16-wind compass rose

  • The eight half-winds are the direction points obtained by bisecting the angles between the principal winds. The half-winds are north-northeast (NNE), east-northeast (ENE), east-southeast (ESE), south-southeast (SSE), south-southwest (SSW), west-southwest (WSW), west-northwest (WNW) and north-northwest (NNW). The name of each half-wind is constructed by combining the names of the principal winds to either side, with the cardinal wind coming first and the ordinal wind second.
  • The eight principal winds and the eight half-winds together form the 16-wind compass rose, with each compass point at a ​22 1⁄2° angle from its two neighbours.
32-point compass rose
32-wind compass card, with English names

32-wind compass rose

  • All of the points in the 16-wind compass rose (above) plus the sixteen quarter-winds (listed below) together form the 32-wind compass rose.
  • The sixteen quarter-winds are the direction points obtained by bisecting the angles between the points on the 16-wind compass rose. The quarter-winds are: (in the first quadrant) north by east (NbE), northeast by north (NEbN), northeast by east (NEbE), and east by north (EbN); (in the second quadrant) east by south (EbS), southeast by east (SEbE), southeast by south (SEbS), and south by east (SbE); (in the third quadrant) south by west (SbW), southwest by south (SWbS), southwest by west (SWbW), and west by south (WbS); (in the fourth quadrant) west by north (WbN), northwest by west (NWbW), northwest by north (NWbN), and north by west (NbW).[4][5]
  • The name of a quarter-wind is "X by Y", where X is a principal wind and Y is a cardinal wind. As a mnemonic device, it is useful to think of "X by Y" as a shortcut for the phrase "one quarter-wind from X towards Y", where a "quarter" is ​11 1⁄4°, X is the nearest principal wind, and Y is the next (more distant) cardinal wind. So, for example, "northeast by east" means "one quarter from NE towards E", "southwest by south" means "one quarter from SW towards S", etc.

In summary, the 32-wind compass rose is yielded from the eight principal winds, eight half-winds and sixteen quarter-winds combined together, with each compass direction point at an ​11 1⁄4° angle from the next.

In the mariner's exercise of boxing the compass, all thirty-two points of the compass are named in clockwise order.[6]

Traditional names

The traditional compass rose of eight winds (and its 16-wind and 32-wind derivatives) was invented by seafarers in the Mediterranean Sea during the Middle Ages (with no obvious connection to the twelve classical compass winds of the ancient Greeks and Romans). The traditional mariner's wind names were expressed in Italian, or more precisely, the Italianate Mediterranean lingua franca common among sailors in the 13th and 14th centuries, which was principally composed of Genoese (Ligurian), mixed with Venetian, Sicilian, Provençal, Catalan, Greek and Arabic terms from around the Mediterranean basin.

32-wind compass with traditional names (and traditional colour code)

This Italianate patois was used to designate the names of the principal winds on the compass rose found in mariners' compasses and portolan charts of the 14th and 15th centuries. The "traditional" names of the eight principal winds are:

  • (N) – Tramontana
  • (NE) – Greco (or Bora in some Venetian sources)
  • (E) – Levante (sometimes Oriente)
  • (SE) – Scirocco (or Exaloc in Catalan)
  • (S) – Ostro (or Mezzogiorno in Venetian)
  • (SW) – Libeccio (or Garbino, Eissalot in Provençal)
  • (W) – Ponente (or Zephyrus in Greek)
  • (NW) – Maestro (or Mistral in Provençal)

Local spelling variations are far more numerous than listed, e.g. Tramutana, Gregale, Grecho, Sirocco, Xaloc, Lebeg, Libezo, Leveche, Mezzodi, Migjorn, Magistro, Mestre, etc. Traditional compass roses will typically have the initials T, G, L, S, O, L, P, and M on the main points. Portolan charts also colour-coded the compass winds: black for the eight principal winds, green for the eight half-winds, and red for the sixteen quarter-winds.

Each half-wind name is simply a combination of the two principal winds that it bisects, with the shortest name usually placed first, for example: NNE is "Greco-Tramontana"; ENE is "Greco-Levante"; SSE is "Ostro-Scirocco", etc. The quarter winds are expressed with an Italian phrase, "Quarto di X verso Y" (pronounced [ˈkwarto di X ˈvɛrso Y][7][8][9] one quarter from X towards Y), or "X al Y" (X to Y) or "X per Y" (X by Y). There are no irregularities to trip over; the closest principal wind always comes first, the more distant one second, for example: north-by-east is "Quarto di Tramontana verso Greco"; and northeast-by-north is "Quarto di Greco verso Tramontana".

32 compass points

The table below shows how the 32 compass points are named.

Each point has an angular range of 11.250 degrees where: middle azimuth is the horizontal angular direction (from north) of the given compass bearing; minimum is the lower angular limit of the compass point; and maximum is the upper angular limit of the compass point.

No. Compass point Abbreviation Traditional wind point Minimum Middle azimuth Maximum
0 North N Tramontana 354.375° 0.000° 5.625°
1 North by east NbE Quarto di Tramontana verso Greco 5.625° 11.250° 16.875°
2 North-northeast NNE Greco-Tramontana 16.875° 22.500° 28.125°
3 Northeast by north NEbN Quarto di Greco verso Tramontana 28.125° 33.750° 39.375°
4 Northeast NE Greco 39.375° 45.000° 50.625°
5 Northeast by east NEbE Quarto di Greco verso Levante 50.625° 56.250° 61.875°
6 East-northeast ENE Greco-Levante 61.875° 67.500° 73.125°
7 East by north EbN Quarto di Levante verso Greco 73.125° 78.750° 84.375°
8 East E Levante 84.375° 90.000° 95.625°
9 East by south EbS Quarto di Levante verso Scirocco 95.625° 101.250° 106.875°
10 East-southeast ESE Levante-Scirocco 106.875° 112.500° 118.125°
11 Southeast by east SEbE Quarto di Scirocco verso Levante 118.125° 123.750° 129.375°
12 Southeast SE Scirocco 129.375° 135.000° 140.625°
13 Southeast by south SEbS Quarto di Scirocco verso Ostro 140.625° 146.250° 151.875°
14 South-southeast SSE Ostro-Scirocco 151.875° 157.500° 163.125°
15 South by east SbE Quarto di Ostro verso Scirocco 163.125° 168.750° 174.375°
16 South S Ostro 174.375° 180.000° 185.625°
17 South by west SbW Quarto di Ostro verso Libeccio 185.625° 191.250° 196.875°
18 South-southwest SSW Ostro-Libeccio 196.875° 202.500° 208.125°
19 Southwest by south SWbS Quarto di Libeccio verso Ostro 208.125° 213.750° 219.375°
20 Southwest SW Libeccio 219.375° 225.000° 230.625°
21 Southwest by west SWbW Quarto di Libeccio verso Ponente 230.625° 236.250° 241.875°
22 West-southwest WSW Ponente-Libeccio 241.875° 247.500° 253.125°
23 West by south WbS Quarto di Ponente verso Libeccio 253.125° 258.750° 264.375°
24 West W Ponente 264.375° 270.000° 275.625°
25 West by north WbN Quarto di Ponente verso Maestro 275.625° 281.250° 286.875°
26 West-northwest WNW Maestro-Ponente 286.875° 292.500° 298.125°
27 Northwest by west NWbW Quarto di Maestro verso Ponente 298.125° 303.750° 309.375°
28 Northwest NW Maestro 309.375° 315.000° 320.625°
29 Northwest by north NWbN Quarto di Maestro verso Tramontana 320.625° 326.250° 331.875°
30 North-northwest NNW Maestro-Tramontana 331.875° 337.500° 343.125°
31 North by west NbW Quarto di Tramontana verso Maestro 343.125° 348.750° 354.375°
32 North N Tramontana 354.375° 360.000° 5.625°

Half- and quarter-points

Compass rose from "American Practical Navigator" 1916

By the middle of the 18th century, the 32-point system had been further extended by using half- and quarter-points to give a total of 128 directions.[3] These fractional points are named by appending, for example 1/4east, 1/2east, or 3/4east to the name of one of the 32 points. Each of the 96 fractional points can be named in two ways, depending on which of the two adjoining whole points is used, for example, N3/4E is equivalent to NbE1/4N. Either form is easily understood but alternative conventions as to correct usage developed in different countries and organisations. "It is the custom in the United States Navy to box from north and south toward east and west, with the exception that divisions adjacent to a cardinal or inter-cardinal point are always referred to that point."[10] The Royal Navy used the additional "rule that quarter points were never read from a point beginning and ending with the same letter."[11]

Compass roses very rarely named the fractional points and only showed small, unlabelled markers as a guide for helmsmen.

128 compass directions

The table below shows how each of the 128 directions are named. The first two columns give the number of points and degrees clockwise from north. The third gives the equivalent bearing to the nearest degree from north or south towards east or west. The "CW" column gives the fractional-point bearings increasing in the clockwise direction and "CCW" counterclockwise. The final three columns show three common naming conventions: No "by" avoids the use of "by" with fractional points; "USN" is the system used by the US Navy; and "RN" is the Royal Navy system. Colour coding shows whether each of the three naming systems matches the "CW" or "CCW" column.

See also

References

  1. ↑ David Boardman. Graphicacy and Geography Teaching, 1983. Page 41 "In particular they should learn that wind direction is always stated as the direction from which, and not to which, the wind is blowing. Once children have grasped these eight points they can learn the full sixteen points of the compass."
  2. ↑ Evans, Frederick John (1859). "Notes on the Magnetism of Ships". Pamphlets on British shipping. 1785–1861. By unknown editor. p. 8 (p. 433 of PDF). ISBN 0-217-85167-3. A deviation table having been formed by any of the processes now.so generally understood, either on the thirty-two points of the compass, the sixteen intermediate, or the eight principal points
  3. 1 2 E. Chambers Cyclopaedia: or, an Universal Dictionary of Arts and Science, 5th Ed, 1743, pp. 206–7, "Points of the Compass, or Horizon, &c., in Geography and Navigation, are the points of division when the whole circle, quite around, is divided into 32 equal parts. These points are therefore at the distance of the 32d part of the circult, or 11° 15′, from each other; hence 5° 37 1/2′ is the distance of the half points and 2° 48 3/4′ is the distance of the quarter points.
  4. ↑ Compass rose at geography.about.com
  5. ↑ Washington Education
  6. ↑ George Payn Quackenbos A Natural Philosophy: Embracing the Most Recent Discoveries 1860 "Mentioning the mariner's compass: the points of the compass in their order is called boxing the compass. — The compass box is suspended within a larger box by means of two brass hoops, or gimbals as they are called, supported at opposite ..."
  7. ↑ "Wordreference.com's entry for 'quarto'".
  8. ↑ "Wordreference.com's entry for 'di'".
  9. ↑ "Wordreference.com's entry for 'verso'".
  10. ↑ Bowditch, Nathaniel (1916). American Practical Navigator: An Epitome of Navigation and Nautical Astronomy. United States Hydrographic Office. p. 15.
  11. ↑ Kemp, Peter, ed. (1988). "Box the Compass". The Oxford Companion to Ships and the Sea. Oxford University Press. p. 103. ISBN 0-19-282084-2.
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