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Chain (unit)
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Chain (unit)
The chain (abbreviated ch) is a unit of length equal to 66 feet (22 yards), used in both the US customary and Imperial unit systems. It is subdivided into 100 links. There are 10 chains in a furlong, and 80 chains in one statute mile. 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.
The chain has been used since the early 17th century in England, and was brought by British settlers during the colonial period to other countries around the globe. 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; 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. In India, "metric chains" of exactly 20 metres (65.62 feet) are used, along with fractions thereof.
The UK statute chain is 22 yards, which is 66 feet (20.1168 m). This unit is a statute measure in the United Kingdom, defined in the Weights and Measures Act 1985. One link is a hundredth part of a chain, which is 7.92 inches (20.1168 cm).
The surveyor's chain first appears in an illustration in a Dutch map of 1607, and in an English book for surveyors of 1610. In 1593 the English mile was redefined by a statute of Queen Elizabeth I as 5,280 feet, to tie in with agricultural practice. In 1620, the polymath Edmund Gunter developed a method of accurately surveying land using a surveyor's chain 66 feet long with 100 links. The 66-foot unit, which was four perches or rods, took on the name the chain. By 1675 it was accepted, and Ogilby wrote:
...a Word or two of Dimensurators or Measuring Instruments, whereof the most usual has been the Chain, and the common length for English Measures 4 Poles, as answering indifferently to the English Mile and Acre, 10 such Chains in length making a Furlong, and 10 single square Chains an Acre, so that a square Mile contains 640 square Acres...
— John Ogilby, Britannia, 1675
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. In 1784 Thomas Jefferson wrote a report for the Continental Congress 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.
The chain is the unit of linear measurement for the survey of the public lands as prescribed by law. All returns of measurement in the rectangular system are made in the true horizontal distance in links, chains, and miles. The only exceptions to this rule are special requirements for measurement in feet in mineral surveys and townsite surveys.
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Chain (unit)
The chain (abbreviated ch) is a unit of length equal to 66 feet (22 yards), used in both the US customary and Imperial unit systems. It is subdivided into 100 links. There are 10 chains in a furlong, and 80 chains in one statute mile. 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.
The chain has been used since the early 17th century in England, and was brought by British settlers during the colonial period to other countries around the globe. 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; 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. In India, "metric chains" of exactly 20 metres (65.62 feet) are used, along with fractions thereof.
The UK statute chain is 22 yards, which is 66 feet (20.1168 m). This unit is a statute measure in the United Kingdom, defined in the Weights and Measures Act 1985. One link is a hundredth part of a chain, which is 7.92 inches (20.1168 cm).
The surveyor's chain first appears in an illustration in a Dutch map of 1607, and in an English book for surveyors of 1610. In 1593 the English mile was redefined by a statute of Queen Elizabeth I as 5,280 feet, to tie in with agricultural practice. In 1620, the polymath Edmund Gunter developed a method of accurately surveying land using a surveyor's chain 66 feet long with 100 links. The 66-foot unit, which was four perches or rods, took on the name the chain. By 1675 it was accepted, and Ogilby wrote:
...a Word or two of Dimensurators or Measuring Instruments, whereof the most usual has been the Chain, and the common length for English Measures 4 Poles, as answering indifferently to the English Mile and Acre, 10 such Chains in length making a Furlong, and 10 single square Chains an Acre, so that a square Mile contains 640 square Acres...
— John Ogilby, Britannia, 1675
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. In 1784 Thomas Jefferson wrote a report for the Continental Congress 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.
The chain is the unit of linear measurement for the survey of the public lands as prescribed by law. All returns of measurement in the rectangular system are made in the true horizontal distance in links, chains, and miles. The only exceptions to this rule are special requirements for measurement in feet in mineral surveys and townsite surveys.
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