One of the great things about coming into a new industry is getting to grips with all of the latest technology and applications, and digging into some of the details on how to configure systems to commonly agreed standards – there was a previous project where the differing co-ordinate systems placed a large piece of infrastructure in the middle of an ocean. Whilst looking through the ArcGIS Pro desktop app with @JasonBrewington, I found where to set display units (map properties/general/display units) and was mildly disappointed by the lack of options available.

In an impressive piece of synchronicity, the following diagram then popped up in my Twitter feed:  (h/t Rob Manual)

Irresistibly, the eye is drawn to an unfamiliar name and were off down the rabbit hole. Who was Gunter? And what was his chain? And how was it different from Ramsden’s?

Turns out, Gunter’s chain was responsible for a lot of the United States as it’s known today. Edmund Gunter (1581 – 1626), mathematician, Gresham College Professor of Astronomy, publisher of the notoriously racy beach read ‘Canon Triangulorum, or Table of Artificial Sines and Tangents’ in 1620, always wanted to build better tools for anyone who calculates measurements. To that end, he created his chain, with a total length of 66 feet (22 yards or 1/10^th of a furlong), comprised of 100 wire links (each 7.92 inches), with a tag or tally every 10 links to show the distances from each end. Scale that up to 80 chains and you have a statue mile (1760 yards).

It quickly became the de-facto measuring tool until the end of the 1800’s (mainly thanks to the Land Ordinance of 1785, originally proposed by Thomas Jefferson, which mandated the use of the chain) for surveyors, whose job was to measure out land that was to be transferred from the crown or government into private ownership. Each chain was hand-made, and despite surveyors and chain men (the persons who actually held the chain) taking an oath to be “faithful, accurate, and … record their results without favor” , an extra link or two was often inserted, to benefit the recipient – modern measuring techniques show that land parcels are often larger than originally described.

The chain process manages to unite two previously incompatible measurements systems (traditional English land units, based on the number four) and decimal (based on 10)). Tying nicely into a conversation with a colleague recently about legacy mains and services plates, the use of the chain-based measuring system was one of the main factors for the US not adopting the metric system as developed by the French in 1790. Despite the first patent (#45,372) for a spring-return steel tape measure being issued in 1860, the chain remained in use through the early part of the twentieth century and is still used today in the British railway system to identify the location of features as being xx chains from a zero point. Distances on township plat maps by the US General Land Office are still shown in chains due to backwards database compatibility. More pertinently for sports fans, the distance between the stumps on a cricket pitch is exactly one chain.

Further reading, including a lovely description of how colonial Williamsburg was laid out around the chain.

Next time, we may delve further into the fantastic knowledge that there are a variety of different “Perches”, the English, the woodland, the church-land and the forest, along with the Irish/plantation and the Scotch, almost none of which are the same length. Or we may not, there’s a lot of facts about maps out there. We’ll very likely talk more about the Ramsden chain as it links to the massively nostalgic (for the British) subject of Ordnance Survey maps. There is a rumour that someone was able to configure ArcGIS Pro to show distance in cubits, I haven’t found out how to do that, still looking.