Mile

!colspan=2 m

mile
international !	colspan=2 |US survey !! colspan=2 |nautical
	km	|	km	1.852	km
1,609.344	|	1,609.347	m	1,852	m

, Scotland, with distances in miles and the wording in both Scottish Gaelic and English.]] A mile is a unit of length, most commonly 5,280 feet (1,760 yards, or about 1,609.3 metres). The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile (1,852 metres, about 6,076.1 feet). There have also been many historical miles and similar units in other systems that may be translated as miles in English; they have varied in length between one and fifteen kilometres.

The exact length of the land mile varied slightly among English-speaking countries until an international agreement in 1959 established the yard as exactly 0.9144 metres, giving a mile of exactly 1,609.344 metres. The United States adopted this international mile for most purposes, but retained the pre-1959 mile for some land-survey data, terming it the US survey mile. In the US, statute mile formally refers to the survey mile, which is about 3.2 mm (⅛ inch) longer than the international mile; however, for most purposes, the difference is insignificant, and statute mile can be used for either the survey mile or the international mile.

The use of the mile as a unit of measurement is now largely confined to the United Kingdom and the US.

Origin

The word mile originally derives from the Old English word mīl which in turn was ultimately derived from the Latin word millia meaning "thousand". The English mile is derived from the Latin mille passuum (one thousand paces) but in other countries the word "mile" (meile in German, mijl in Dutch) was derived from the Latin miliarium spatium (one thousand "intervals").

Roman mile

The Romans were first to use the unit of long distance (literally "a thousand paces" in Latin, where each pace was two steps). It denoted a distance of 1,000 paces or 5,000 Roman feet, and is estimated to be about 1,479 metres (1,617 yards). This unit that is now known as the . spread throughout the Roman Empire, often with modifications to fit local systems of measurements.

Historical miles in the Arabic world and Europe

The Arab mile (or Arabic mile) was a unit of length used by medieval Muslim geographers. Its precise length is uncertain, but is believed to be around 1925 metres. The Danish (traditional) was 24,000 Danish feet or 7532.5 metres. Sometimes it was interpreted as exactly 7.5 kilometres. It is the same as the north German (below). The was a traditional unit in German-speaking countries. It was 24,000 German feet; the SI equivalent was 7586 metres in Austria or 7532.5 metres in northern Germany. There was a version known as the , which was 4 Admiralty nautical miles, 7,412.7 metres, or 1/15 of a degree of latitude. In Norway and Sweden, a mil is a unit of length equal to 10 kilometres and commonly used in everyday language. However in more formal situations, such as on road signs and when there is risk of confusion with English miles, kilometres are used instead. The traditional Swedish spanned the range from 6000-14,485 metres, depending on province. It was however standardized in 1649 to 36,000 Swedish feet, or 10.687 km. The Russian was a traditional Russian unit of distance, equal to 7 verst, or 7.468 km. The (Croatian mile) is 11,130 metres = 11.13 km = 1/10 of equator's degree, first used by Jesuit Stjepan Glavač on a map from 1673. The (also called ) (mile of Croatian Ban, Croatian mile) was 7586 metres = 7.586 kilometres, or 24,000 feet (the same as the Austrian mile).

Historical miles in Britain and Ireland

The statute mile (1592) of Elizabeth I was not the only definition of the mile in Britain and Ireland. Perhaps the earliest tables of English linear measures, Arnold's Customs of London (c. 1500) indicates a mile consisted of 8 furlongs, each of 625 feet, for a total of 5000 feet (1666⅔ yards, 0.947 statute miles, 1524 metres): The seventeenth century cartographer Robert Morden had multiple scales on his maps - for example his map of Hampshire showed two different miles that had a ratio of and his map of Dorset had three scales with a ratio of . In both cases, the smallest mile appears to be the statute mile.

Scots mile

The Royal Mile in Edinburgh, i.e., from the Castle down to Holyrood Abbey, is approximately the same length as the Scots mile. English miles were imposed in 1824 by an Act of Parliament.

Equivalent to:

Scottish measures: 320 falls; or 8 Scots furlongs

Metric system: 1807 metres

Imperial system: 1,976 yards (about 1.12 miles)

Robert Burns spoke of Scots miles in the first verse of Tam O' Shanter

:"While we sit bousing at the nappy, :An' getting fou and unco happy, :We think na on the lang Scots miles, :The mosses, waters, slaps and stiles, :That lie between us and our hame, :Where sits our sulky, sullen dame, :Gathering her brows like gathering storm, :Nursing her wrath to keep it warm."

The Scots mile was longer than the English mile, but varied in length from place to place. It was formally abolished by an Act of the Parliament of Scotland in 1685, and again by the Treaty of Union with England in 1707, but continued in use as a customary unit during the 18th century. It was obsolete by the time of its final abolition by the Weights and Measures Act 1824. As there are 320 rods in a mile and 1.0016 Imperial inches in a Scots inch, this would make the Scots mile equal to 5,920 Scots feet (1,976.5 imperial yards, 1.12 statute miles). Other estimates are similar.

Irish mile

The Irish mile was longer still. Again, the difference arose from a different length of the rod in Ireland (usually called the perch locally): 21 feet as opposed to 16½ feet in England.

From 1774, through the 1801 union with Britain, until the 1820s, the grand juries of 25 Irish counties commissioned surveyed maps at scales of one or two inches per Irish mile. Scottish engineer William Bald's County Mayo maps of 1809–30 were drawn in English miles and rescaled to Irish miles for printing. The Howth–Dublin Post Office extension of the London–Holyhead turnpike engineered by Thomas Telford had mileposts in English miles. Although legally abolished by the Weights and Measures Act 1824, the Irish mile was used till 1856 by the Irish Post Office. The Ordnance Survey of Ireland, from its establishment in 1824, used English miles.

In 1894, Alfred Austin complained after visiting Ireland that "the Irish mile is a fine source of confusion when distances are computed. In one county a mile means a statute mile, in another it means an Irish mile". When the Oxford English Dictionary definition of "mile" was published in 1906, it described the Irish mile as "still in rustic use". Variation in signage persisted till the publication of standardised road traffic regulations by the Irish Free State in 1926. In 1937, a man prosecuted for driving outside the 15-mile limit of his licence offered the unsuccessful defence that, since the state was independent, the limit ought to use Irish miles, "just as no one would ever think of selling land other than as Irish acres". A 1965 proposal by two TDs to replace statute miles with Irish miles in a clause of the Road Transport Act was rejected. The term is now obsolete as a specific measure, though an "Irish mile" colloquially is a long but vague distance akin to a "country mile".

== Statute mile == The statute mile was so-named because it was defined by an English Act of Parliament in 1592, during the reign of Queen Elizabeth I. It was defined as being 1,760 yards (5,280 feet, about 1609 metres). For surveying, the statute mile is divided into eight furlongs; each furlong into ten chains; each chain into four rods (also known as poles or perches); and each rod into 25 links. This makes the rod equal to 5½ yards or 16½ feet in both Imperial and US usage.

The exact conversion of the mile to SI units depends on which definition of the yard is used. Different English-speaking countries maintained independent physical standards for the yard that were found to differ by small, but measurable, amounts and even to slowly shorten in length. The U.S. redefined the U.S. yard in 1893, but this resulted in US and Imperial measures of distance having very slightly different lengths. The difference was resolved in 1959 with the definition of the international yard in terms of the metre by Australia, Canada, New Zealand, South Africa, the UK and the US. The "international mile" of 1,760 international yards is exactly 1,609.344 metres.

The difference from the previous standards was 2 ppm, or about 3.2 millimetres (⅛ inch) per mile. The US standard was slightly longer and the old Imperial standards had been slightly shorter than the international mile. When the international mile was introduced in English-speaking countries, the basic geodetic datum in North America was the North American Datum of 1927 (NAD27). This had been constructed by triangulation based on the definition of the foot in the Mendenhall Order of 1893, with 1 foot =  metres and the definition was retained for data derived from NAD27, but renamed the US survey foot to distinguish it from the international foot.

The US survey mile is 5280 survey feet, or about 1609.3472 metres. In the US, statute mile formally refers to the survey mile, but for most purposes, the difference between the survey mile and the international mile is insignificant—one international mile is exactly 0.999998 of a US survey mile—so statute mile can be used for either. But in some cases, such as in the US State Plane Coordinate Systems (SPCSs), which can stretch over hundreds of miles, the accumulated difference can be significant, so it is important to note that the reference is to the US survey mile.

The North American Datum of 1983 (NAD83), which replaced the NAD27, is defined in metres. State Plane Coordinate Systems were then updated, but the National Geodetic Survey left individual states to decide which (if any) definition of the foot they would use. All State Plane Coordinate Systems are defined in metres, and 42 of the 50 states only use the metre-based State Plane Coordinate Systems. However, eight states also have State Plane Coordinate Systems defined in feet, seven of them in US Survey feet and one in international feet. However, The current National Topographic Database of the Survey of India is based on the metric WGS-84 datum, which is also used by the Global Positioning System.

Metric mile

The term metric mile is used in sports such as track and field athletics and speed skating to denote a distance of 1500 metres (about 4921 ft). In United States high school competition, the term is sometimes used for a race of 1,600 metres (about 5249 ft).

Nautical mile

– the analog of a line in spherical trigonometry– and hence the shortest path connecting two points on the globular surface. Meridians are great circles that pass through the poles.]]

The nautical mile was originally defined as one minute of arc along a meridian arc of the Earth. It is a convenient reference, since it is fairly constant at all latitudes, in contrast with degrees of longitude which vary from 60 NM at the equator to zero at the poles.

Navigators use dividers to step off the distance between two points on the navigational chart, then place the open dividers against the minutes-of-latitude scale at the edge of the chart, and read off the distance in nautical miles. Since it is now known that the Earth is not perfectly spherical but an oblate spheroid, the length derived from this method varies slightly from the equator to the poles. For instance, using the WGS84 Ellipsoid, the commonly accepted Earth model for many purposes today, one minute of latitude at the WGS84 equator is 6,087 feet and at the poles is 6,067 feet. On average, it is about 6,076 feet (about 1,852 metres or 1.15 statute miles).

In the United States, the nautical mile was defined in the nineteenth century as 6,080.2 feet (1,853.249 m), whereas in the United Kingdom, the Admiralty nautical mile was defined as 6,080 feet (1,853.184 m) and was approximately one minute of latitude in the latitudes of the south of the UK. Other nations had different definitions of the nautical mile, but it is now internationally defined to be exactly 1,852 metres.

Related nautical units

The nautical mile per hour is known as the knot. Nautical miles and knots are almost universally used for aeronautical and maritime navigation, because of their relationship with degrees and minutes of latitude and the convenience of using the latitude scale on a map for distance measuring.

The data mile is used in radar-related subjects and is equal to 6,000 feet (1.8288 kilometres). The radar mile is a unit of time (in the same way that the light year is a unit of distance), equal to the time required for a radar pulse to travel a distance of two miles (one mile each way). Thus, the radar statute mile is 10.8 μs and the radar nautical mile is 12.4 μs.

Abbreviation and symbol

There have been several abbreviations for mile (with and without trailing period): mi, ml, m, M. In the United States, the National Institute of Standards and Technology now uses and recommends mi, which avoids confusion with metres, millilitres, etc., but in everyday usage (at least in the United States and in the United Kingdom), units such as miles per hour and miles per gallon are almost always abbreviated as mph or mpg (rather than mi/h or mi/gal).

Grid system

Cities in the continental United States often have streets laid out by miles. Detroit, Indianapolis, Chicago, Phoenix, Philadelphia, Las Vegas, Los Angeles, and Miami, are several examples. Typically the largest streets are about a mile apart, with others at half-mile and quarter-mile intervals. Also in the Manhattan borough of New York City, "streets" are almost exactly 20 per mile, while the major numbered "avenues" are about six per mile.

Idioms

Even in English-speaking countries that have moved from the Imperial to the metric system (for example, Australia and New Zealand), the mile is still used in a variety of idioms. These include:

A is used colloquially to denote a very long distance.

"A miss is as good as a mile" (failure by a narrow margin is no better than any other failure)

"Give him an inch and he'll take a mile" - a corruption of "Give him an inch and he'll take an ell" (the person in question will become greedy if shown generosity)

"Missed by a mile" (missed by a wide margin)

"Talk a mile a minute" (speak at a rapid rate)

"To go the extra mile" (to put in extra effort)

"Miles away" (lost in thought, or daydreaming)

"Milestone" (an event indicating significant progress)

See also

Anthropic units

Data mile

Fibonacci sequence for miles converting to kilometers

Food miles

Four-minute mile

Geographical mile

Mile run

Section lines

Square mile

United States customary units

Notes

References

American Heritage Dictionary of the English Language (3rd ed.) (1992). Boston: Houghton Mifflin Company.

American Heritage Dictionary of the English Language (4th ed.) (2006). Boston: Houghton Mifflin Company. ISBN 978-0-618-70172-8.

Astin. V. and H. Arnold Karo. (1959). Refinement of values for the yard and the pound, Washington DC: National Bureau of Standards, republished on National Geodetic Survey web site and the Federal Register (Doc. 59-5442, Filed, June 30, 1959, 8:45 a.m.)

Barbrow, Louis E. and Lewis V. Judson (1976). Weights and Measures Standards of the United States – A Brief History. National Institute of Standards and Technology.

Butcher, Tina; et al. ed. (2007). NIST Handbook 44: Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. Appendix C, p. C-13.

Klein, Herbert Arthur (1974, corrected 1988). The Science of Measurement: A Historical Survey. New York: Dover. (previously published by Simon & Schuster under the title The World of Measurements: Masterpieces, Mysteries and Muddles of Metrology)

Maloney, Elbert S. (1978). Dutton's Navigation and Piloting. 13th Ed. Annapolis: Naval Institute Press.

Rowlett, Russ (2005). How Many? A Dictionary of Units of Measurement. Faculty member's web page at University of North Carolina at Chapel Hill. Retrieved November 10, 2007.

Thompson, Ambler, and Taylor, Barry. (2008). Guide for the Use of the International System of Units (SI) (PDF format; requires Adobe Reader. (Special Publication 811). Gaithersburg, MD: National Institute of Standards and Technology.

External links

NIST General Tables of Units of Measurement

Category:Units of length Category:Imperial units Category:Customary units in the United States Category:Ancient Roman geography Category:Surveying Category:Roman Inventions Category:Royal Mile Category:Scottish weights and measures