Chain (unit)

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.

[9] 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 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.

[13] 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.

Since railways are linear in topology, the "mileage" or "chainage" is sufficient to identify a place uniquely on any given route.

On new railway lines built in the United Kingdom such as High Speed 1, the position along the alignment is still referred to as "chainage", although the value is now expressed in metres.

Chains and links are commonly encountered in older metes and bounds legal descriptions.

Distances on township plat maps made by the US General Land Office are shown in chains.

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.

[21][22] 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.

In the Southwestern United States, the vara chain also called the Texas chain, of 20 varas (16.9164 m , or 55+1⁄2 ft) was used in surveying Spanish and later Mexican land grants, such as the major Fisher–Miller and Paisano Grants in Texas, several similarly large ones in New Mexico, and over 200 smaller ranchos in California.

[clarification needed] Another version used extensively in forestry and surveying is the hip-chain: a small box containing a string counter, worn on the hip.

Location marker painted on a British railway bridge, showing 112 miles and 63 chains; photograph taken August 2007