The chain is a
unit
Unit may refer to:
Arts and entertainment
* UNIT, a fictional military organization in the science fiction television series ''Doctor Who''
* Unit of action, a discrete piece of action (or beat) in a theatrical presentation
Music
* ''Unit'' (alb ...
of
length
Length is a measure of distance. In the International System of Quantities, length is a quantity with dimension distance. In most systems of measurement a base unit for length is chosen, from which all other units are derived. In the Interna ...
equal to 66
feet
The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made ...
(22
yards
The yard (symbol: yd) is an English unit of length in both the British imperial and US customary systems of measurement equalling 3 feet or 36 inches. Since 1959 it has been by international agreement standardized as exactly 0.914 ...
). It is subdivided into 100
links[ (PDF)] or 4
rods. There are 10 chains in a
furlong
A furlong is a measure of distance in imperial units and United States customary units equal to one eighth of a mile, equivalent to 660 feet, 220 yards, 40 rods, 10 chains or approximately 201 metres. It is now mostly confined to use in hors ...
, and 80 chains in one
statute mile
The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and United States customary unit of distance; both are based on the older English unit of length equal to 5,280 Engli ...
.
In metric terms, it is 20.1168
m long.
By extension, chainage (running distance) is the distance along a curved or straight survey line from a fixed commencing point, as given by an
odometer
An odometer or odograph is an instrument used for measuring the distance traveled by a vehicle, such as a bicycle or car. The device may be electronic, mechanical, or a combination of the two (electromechanical). The noun derives from ancient Gr ...
.
The chain has been used for several centuries in England and in some other countries influenced by English practice. In the United Kingdom, there were 80 chains to the mile, but until the early nineteenth century the
Scottish and Irish customary miles were longer than the
statute mile
The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and United States customary unit of distance; both are based on the older English unit of length equal to 5,280 Engli ...
; consequently a Scots chain was about 74 (imperial) feet, an Irish chain 84 feet. These longer chains became obsolete following the adoption of
the imperial system of units in 1824.
Definition
The UK statute chain is 22 yards, which is . This unit is a
statute measure
Weights and measures acts are acts of the British Parliament determining the regulation of weights and measures. It also refers to similar royal and parliamentary acts of the Kingdoms of England and Scotland and the medieval Welsh states. T ...
in the United Kingdom, defined in the
Weights and Measures Act 1985
Weights and measures acts are acts of the British Parliament determining the regulation of weights and measures. It also refers to similar royal and parliamentary acts of the Kingdoms of England and Scotland and the medieval Welsh states. T ...
.
[
] One link is a hundredth part of a chain, which is .
[
]
Origin
The surveyor's chain was first mentioned 1579 and appears in an illustration in 1607. In 1593 the English mile
The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and United States customary unit of distance; both are based on the older English unit of length equal to 5,280 English ...
was redefined by a statute of Queen Elizabeth I
Elizabeth I (7 September 153324 March 1603) was Queen of England and Ireland from 17 November 1558 until her death in 1603. Elizabeth was the last of the five House of Tudor monarchs and is sometimes referred to as the "Virgin Queen".
El ...
as 5,280 feet, to tie in with agricultural practice. In 1620, the polymath
A polymath ( el, πολυμαθής, , "having learned much"; la, homo universalis, "universal human") is an individual whose knowledge spans a substantial number of subjects, known to draw on complex bodies of knowledge to solve specific pro ...
Edmund Gunter
Edmund Gunter (158110 December 1626), was an English clergyman, mathematician, geometer and astronomer of Welsh descent. He is best remembered for his mathematical contributions which include the invention of the Gunter's chain, the Gunter's qu ...
developed a method of accurately surveying land using a surveyor's chain 66 feet long with 100 links. The 66 feet unit, which was four perches or rods, took on the name the chain. By 1675 it was accepted, and Ogilby wrote:
From Gunter's system, the chain and the link became standard surveyors' units of length and crossed to the colonies. The thirteen states of America were expanding westward and the public land had to be surveyed for a cadastral
A cadastre or cadaster is a comprehensive recording of the real estate or real property's metes-and-bounds of a country.Jo Henssen, ''Basic Principles of the Main Cadastral Systems in the World,'/ref>
Often it is represented graphically in a cad ...
. In 1784 Thomas Jefferson
Thomas Jefferson (April 13, 1743 – July 4, 1826) was an American statesman, diplomat, lawyer, architect, philosopher, and Founding Fathers of the United States, Founding Father who served as the third president of the United States from 18 ...
wrote a report for the Continental Congress
The Continental Congress was a series of legislative bodies, with some executive function, for thirteen of Britain's colonies in North America, and the newly declared United States just before, during, and after the American Revolutionary War. ...
proposing the rectangular survey system; it was adopted with some changes as the Land Ordinance of 1785 on 20 May the following year. In the report, the use of the chain as a unit of measurement was mandated, and the chain was defined.
Modern use and historic cultural references
Britain
In Britain, the chain is no longer used for practical survey work. However, it survives on the railways of the United Kingdom as a location identifier. When railways were designed, the location of features such as bridges and stations was indicated by a cumulative longitudinal "mileage", using miles and chains, from a zero point at the origin or headquarters of the railway, or the originating junction of a new branch line. Since railways are entirely linear in topology, the "mileage" or "chainage" is sufficient to identify a place uniquely on any given route. Thus a certain bridge location may be indicated as 112 miles and 63 chains (181.51 km) from the origin. In the case of the photograph the bridge is near Keynsham
Keynsham ( ) is a town and civil parish located between Bristol and Bath in Somerset, England. It has a population of 16,000.
It was listed in the Domesday Book as ''Cainesham'' (as it is pronounced), which is believed to mean the home of Sai ...
, that distance from London Paddington station
Paddington, also known as London Paddington, is a Central London railway terminus and London Underground station complex, located on Praed Street in the Paddington area. The site has been the London terminus of services provided by the Great W ...
. The indication "MLN" after the mileage is the engineers' line reference describing the route as the Great Western Main Line
The Great Western Main Line (GWML) is a main line railway in England that runs westwards from London Paddington to . It connects to other main lines such as those from Reading to Penzance and Swindon to Swansea. Opened in 1841, it was the or ...
, so that visiting engineers can uniquely describe the bridge they are inspecting, as there may be bridges at 112 miles 63 chains on other routes.
On new railway lines built in the United Kingdom such as High Speed 1
High Speed 1 (HS1), legally the Channel Tunnel Rail Link (CTRL), is a high-speed railway linking London with the Channel Tunnel.
It is part of a line carrying international passenger traffic between the United Kingdom and mainland Europe; ...
, the position along the alignment is still called "chainage" although the value is now defined in metres.
North America
The use of the chain was mandatory in laying out US townships.[ A federal law was passed in 1785 (the Public Land Survey Ordinance) that all official government surveys must be done with a Gunter's (surveyor's) chain. Chains and links are commonly encountered in older ]metes and bounds
Metes and bounds is a system or method of describing land, real property (in contrast to personal property) or real estate. The system has been used in England for many centuries and is still used there in the definition of general boundaries. The ...
legal descriptions. Distances on township plat
In the United States, a plat ( or ) (plan) is a cadastral map, drawn to scale, showing the divisions of a piece of land. United States General Land Office surveyors drafted township plats of Public Lands Surveys to show the distance and bear ...
maps made by the US General Land Office are shown in chains.
Under the US Public Land Survey System
The Public Land Survey System (PLSS) is the surveying method developed and used in the United States to plat, or divide, real property for sale and settling. Also known as the Rectangular Survey System, it was created by the Land Ordinance of 1 ...
, parcels of land
A cadastre or cadaster is a comprehensive recording of the real estate or real property's metes-and-bounds of a country.Jo Henssen, ''Basic Principles of the Main Cadastral Systems in the World,'/ref>
Often it is represented graphically in a cad ...
are often described in terms of the section
Section, Sectioning or Sectioned may refer to:
Arts, entertainment and media
* Section (music), a complete, but not independent, musical idea
* Section (typography), a subdivision, especially of a chapter, in books and documents
** Section sign ...
(), quarter-section (), and quarter-quarter-section (). Respectively, these square divisions of land are approximately 80 chains (one mile or 1.6 km), 40 chains (half a mile or 800 m), and 20 chains (a quarter mile or 400 m) on a side.
The chain is still used in agriculture: measuring wheels with a circumference of 0.1 chain (diameter ≈ 2.1 ft or 64 cm) are still readily available in Canada and the United States. For a rectangular tract, multiplying the number of turns of a chain wheel for each of two adjacent sides and dividing by 1,000 gives the area in acres.
In Canada, road allowances were originally 1 chain wide and are now 20 metres.
The unit was also used in mapping the United States along train routes in the 19th century. Railroad
Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
s in the United States have long since used decimal
The decimal numeral system (also called the base-ten positional numeral system and denary or decanary) is the standard system for denoting integer and non-integer numbers. It is the extension to non-integer numbers of the Hindu–Arabic numeral ...
fractions of a mile. Some subways such as the New York City Subway
The New York City Subway is a rapid transit system owned by the government of New York City and leased to the New York City Transit Authority, an affiliate agency of the state-run Metropolitan Transportation Authority (MTA). Opened on October 2 ...
and the Washington Metro
The Washington Metro (or simply Metro), formally the Metrorail,[Google Books search/preview ...](_blank)
were designed with and continue with a chaining system using the 100-foot engineer's chain.
In the United States, the chain is also used as the measure of the rate of spread of wildfires (chains per hour), both in the predictive National Fire Danger Rating System National Fire Danger Rating System (NFDRS) is used in the United States to provide a measure of the relative seriousness of burning conditions and threat of wildfires.
Background
John J. Keetch, a fire researcher in the southeast, wrote that "One ...
as well as in after-action reports. The term ''chain'' is used by wildland firefighters in day-to-day operations as a unit of distance.
Australia and New Zealand
In Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
and New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, most building lots in the past were a quarter of an acre, measuring one chain by two and a half chains, and other lots would be multiples or fractions of a chain. The street frontage
Frontage is the boundary between a plot of land or a building and the road onto which the plot or building fronts. Frontage may also refer to the full length of this boundary. This length is considered especially important for certain types of ...
s of many houses in these countries are one chain wide—roads were almost always wide in urban areas, sometimes or . Laneways would be half a chain (10.1 m). In rural areas the roads were wider, up to where a stock route
A stock route, also known as travelling stock route (TSR), is an authorised thoroughfare for the walking of domestic livestock such as sheep or cattle from one location to another in Australia. The stock routes across the country are colloquially ...
was required. roads were surveyed as major roads or highways between larger towns, roads between smaller localities, and roads were local roads in farming communities. Roads named Three Chain Road etc. persist today.
The "Queen's Chain" is a concept that has long existed in New Zealand, of a strip of public land, usually 20 metres (or one chain in pre-metric measure) wide from the high water mark, that has been set aside for public use along the coast, around many lakes, and along all or part of many rivers. These strips exist in various forms (including road reserves, esplanade reserves, esplanade strips, marginal strips and reserves of various types) but not as extensively and consistently as is often assumed.
Cricket pitches
The chain also survives as the length of a cricket pitch
In the game of cricket, the cricket pitch consists of the central strip of the cricket field between the wickets. It is long (1 chain) and wide. The surface is flat and is normally covered with extremely short grass, but can be completely d ...
, being the distance between the stumps.
Measuring instruments
Civil engineers and surveyors use various instruments (chains) for measuring distance. Other instruments used for measuring distance include tapes and bands. A steel band is also known as a "band chain".
Surveyors' chain (Gunter's chain)
In 1620, the polymath Edmund Gunter
Edmund Gunter (158110 December 1626), was an English clergyman, mathematician, geometer and astronomer of Welsh descent. He is best remembered for his mathematical contributions which include the invention of the Gunter's chain, the Gunter's qu ...
developed a method of accurately surveying land using a 100 link chain, 66 feet long called the Gunter's Chain. Other surveyors chains have been used historically.
Engineer's chain (Ramsden's chain)
A longer chain of , with a hundred links, was devised in the UK in the late 18th century by Jesse Ramsden
Jesse Ramsden FRS FRSE (6 October 1735 – 5 November 1800) was a British mathematician, astronomical and scientific instrument maker. His reputation was built on the engraving and design of dividing engines which allowed high accuracy measure ...
, though it never supplanted Gunter's chain. Surveyors also sometimes used such a device, and called it the ''engineer's chain''.