Editing Chain (unit) (section)

===North America===
The use of the chain was mandatory in laying out US townships.<ref name=Cazier/> A federal law was passed in 1785 (the [[Public Land Survey System|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]] legal descriptions. Distances on township [[plat]] maps made by the US General Land Office are shown in chains.

Under the US [[Public Land Survey System]], [[Lot (real estate)|parcels of land]] are often described in terms of the [[Section (United States land surveying)|section]] ({{convert|640|acre|ha|0|disp=or}}), quarter-section ({{convert|160|acre|ha|1|disp=or}}), and quarter-quarter-section ({{convert|40|acre|ha|2|disp=or}}). Respectively, these square divisions of land are approximately 80 chains (one mile or 1.6&nbsp;km), 40 chains (half a mile or 800&nbsp;m), and 20 chains (a quarter mile or 400&nbsp;m) on a side.

The chain is still used in agriculture: measuring wheels with a circumference of 0.1 chain (diameter ≈ 2.1&nbsp;ft or 64&nbsp;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.<ref>{{cite news |last1=Lakey |first1=Jack |title=Turns out there is a standard to determine where a homeowner's property ends: The Fixer |url= https://www.thestar.com/yourtoronto/the_fixer/2017/06/21/turns-out-there-is-a-standard-to-determine-where-a-homeowners-property-ends-the-fixer.html |access-date=22 June 2017 |work=[[Toronto Star]] |date=21 June 2017}}</ref>

The unit was also used in mapping the United States along train routes in the 19th century. [[Railroad]]s in the United States have long since {{when|date=July 2018}} used [[decimal]] fractions of a mile. Some subways such as the [[New York City Subway]] and the [[Washington Metro]] were designed with and continue with a [[New York City Subway chaining|chaining system]] using the 100-foot [[engineer's chain]].<ref name=ERA>{{Cite web|url=https://issuu.com/erausa/docs/2017-01-bulletin|title=The ERA Bulletin 2017-01|date=January 18, 2017|website=[[Issuu]]|publisher=Electric Railroaders' Association|access-date=January 18, 2017}}</ref>

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]] 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.<ref>[http://www.fs.fed.us/psw/publications/documents/psw_gtr090/psw_gtr090.pdf Documents]</ref>