Points of the compass explained

The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each separated by 90 degrees, and secondarily divided by four ordinal (intercardinal) directions—northeast, southeast, southwest, and northwest—each located halfway between two cardinal directions. Some disciplines such as meteorology and navigation further divide the compass with additional azimuths. Within European tradition, a fully defined compass has 32 "points" (and any finer subdivisions are described in fractions of points).[1]

Compass points are valuable in that they allow a user to refer to a specific azimuth in a colloquial fashion, without having to compute or remember degrees.[2]

Designations

The names of the compass point directions follow these rules:

8-wind compass rose

16-wind compass rose

32-wind compass rose

In summary, the 32-wind compass rose comes from the eight principal winds, eight half-winds, and sixteen quarter-winds combined, with each compass point at an ° angle from the next.

Half- and quarter-points

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.[6] These fractional points are named by appending, for example, east, east, or east 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, NE is equivalent to NbEN. 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."[7] The Royal Navy used the additional "rule that quarter points were never read from a point beginning and ending with the same letter."[8]

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

Maritime Use

Prior to the modern three-figure method of describing directions (using the 360° of a circle), the 32-point compass was used for directions on most ships, especially among European crews. The smallest unit of measure recognized was 'one point', 1/32 of a circle, or °.[9] In the mariner's exercise of "boxing the compass", all thirty-two points of the compass are named in clockwise order.[10] This exercise became more significant as navigation improved and the half- and quarter-point system increased the number of directions to include in the 'boxing'. Points remained the standard unit until switching to the three-figure degree method. These points were also used for relative measurement, so that an obstacle might be noted as 'two points off the starboard bow', meaning two points clockwise of straight ahead, ° This relative measurement may still be used in shorthand on modern ships, especially for handoffs between outgoing and incoming helmsmen, as the loss of granularity is less significant than the brevity and simplicity of the summary.

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. Colour coding shows whether each of the three naming systems matches the "CW" or "CCW" column.

Traditional Mediterranean compass points

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.

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:

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 as /it/[11] [12] [13] 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".

The table below shows how the 32 compass points are named. Each point has an angular range of degrees where the azimuth midpoint is the horizontal angular direction (clockwise from north) of the given compass bearing; minimum is the lower (counterclockwise) angular limit of the compass point; and maximum is the upper (clockwise) angular limit of the compass point.

Chinese compass points

Navigation texts dating from the Yuan, Ming, and Qing dynasties in China use a 24-pointed compass with named directions. These are based on the twelve Earthly Branches, which also form the basis of the Chinese zodiac. When a single direction is specified, it may be prefaced by the character Chinese: 單 (meaning single) or Chinese: 丹.

Headings mid-way in-between are compounds as in English. For instance, Chinese: 癸子 refers to the direction halfway between point Chinese: 子 and point Chinese: 癸, or °. This technique is referred to as a double-needle (Chinese: 雙針) compass.

PointOrdinal NameAngle
Chinese: 子 zǐnorth0° or 360°
Chinese: 癸 guǐ15°
Chinese: 丑 chǒu30°
Chinese: 艮 gěnnortheast45°
Chinese: 寅 yín60°
Chinese: 甲 jiǎ75°
Chinese: 卯 mǎoeast90°
Chinese: 乙 yǐ105°
Chinese: 辰 chén120°
Chinese: 巽 xùnsoutheast135°
Chinese: 巳 sì150°
Chinese: 丙 bǐng165°
Chinese: 午 wǔsouth180°
Chinese: 丁 dīng195°
Chinese: 未 wèi210°
Chinese: 坤 kūnsouthwest225°
Chinese: 申 shēn240°
Chinese: 庚 gēng255°
Chinese: 酉 yǒuwest270°
Chinese: 辛 xīn285°
Chinese: 戌 xū300°
Chinese: 乾 qiánnorthwest315°
Chinese: 亥 hài330°
Chinese: 壬 rén345°

See also

External links

Notes and References

  1. Book: Pamphlets on British shipping. 1785–1861 . 1859 . 0-217-85167-3 . Evans . Frederick John . Frederick John Owen Evans . 8 (p. 433 of PDF) . Notes on the Magnetism of Ships . 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 . https://books.google.com/books?id=QPNAAAAAIAAJ&pg=RA2-PA50.
  2. Book: Boardman, David . Graphicacy and Geography Teaching . 1983 . 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..
  3. See Wiktionary definitions: north; northeast; east; southeast; south; southwest; west; northwest
  4. Web site: An Overview and History of the Compass. Xanthe. Webb Aintablian. 28 June 2018. Dotdash. thoughtco.com. live. https://web.archive.org/web/20180706191612/https://www.thoughtco.com/the-compass-instrument-1435002. 6 July 2018.
  5. Web site: Compass Rose. Robert E.. Lee. 2011. University of Washington. dead. https://web.archive.org/web/20150221121147/http://staff.washington.edu/rel2/geog100-UW/Scenarios/Rutters/Compass_Rose.html. 21 February 2015.
  6. E. Chambers. Cyclopaedia: or, an Universal Dictionary of Arts and Science, 5th Ed, 1743, pp. 206–207, "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 circuit, or 11° 15′, from each other; hence 5° ′ is the distance of the half points and 2° ′ is the distance of the quarter points.
  7. Book: American Practical Navigator: An Epitome of Navigation and Nautical Astronomy . Bowditch . Nathaniel . United States Hydrographic Office . 1916 . 15 .
  8. Encyclopedia: The Oxford Companion to Ships and the Sea . Kemp . Peter . 1988 . Oxford University Press . 0-19-282084-2 . Box the Compass . 103 . https://archive.org/details/oxfordcompaniont00kemp/page/103.
  9. Web site: Johnson . Tony . 2020-01-05 . Nautical Terminator – Points . 2024-06-29 . Tradewinds Sailing Blog . en-US.
  10. 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 ..."
  11. Web site: quarto. WordReference.com. English translation: fourth, quarter. 2 December 2018.
  12. Web site: di. WordReference.com. English translation: of, from.... 2 December 2018.
  13. Web site: verso. WordReference.com. English translation: towards, toward, close to, near to. 2 December 2018.

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