New York City Subway chaining is a method to precisely specify locations along the New York City Subway lines. It measures distances from a fixed point, called chaining zero, following the twists and
Chaining numbers can be seen on the black pillars in the middle of the tracks of West Fourth Street–Washington Square.
Chain (unit)
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The chain is a unit of length equal to 66 feet, 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
New York City Subway chaining
…distance by the most direct route ("as the crow flies"). The New York City Subway system differs from other railroad chaining systems in that it uses the engineer's chain of 100 feet (30.48 m) rather than the surveyor's chain of 66 feet (20.12 m). Chaining zero is a fixed point from which the chaining is measured on a…
The chain is based on the length of Gunter's chain, which is 66 feet (22 yd) long.
Location marker painted on a British railway bridge, showing 112 miles and 63 chains; photograph taken August 2007
Using a DT Ape