In 1620, an Englishman by the name of Edmund Gunter invented a land surveying device known as Gunter's chain. As the name suggests, it was an actual chain (see above). Each chain contained 100 links and, when fully extended, it measured 66 feet.
This was a monumental innovation as it greatly simplified land surveying and made it a lot easier to measure out acres -- especially if you maybe weren't great with math. So it is perhaps no surprise that this simple device forever changed our cities.
But first, here's the only math you need to know:
Number of chains x number of chains / 10 = number of acres
For example:
A lot measuring 66 feet by 66 feet would mean it has an area of 4,356 square feet, or 0.1 acres (1 acre = 43,560 square feet). It would also mean that this lot measures 1 chain by 1 chain, or 1 square chain. Take 1 square chain and divide it by 10, and you arrive at the same 0.1 acres.
Similarly, a lot measuring 660 feet by 660 feet would mean it has an area of 435,600 square feet, or 10 acres. Using Gunter's chain, this lot is 10 chains by 10 chains, which equals 100 square chains. Divide 100 square chains by 10 and you arrive at the same 10 acres.
Put differently, 1 acre equals 10 square chains in Gunter's system.
Because of its simplicity and utility, the chain became a statutory unit of measurement in England by the 1670s. And as a result, it spread throughout the British Empire, meaning it started to influence how new cities were being planned and laid out.
Let's look at the example of Salt Lake City.
We have spoken before about the city's famously large blocks. They have the dubious distinction of being the largest in the US. But what you may not have noticed is that the typical SLC block measures exactly 660 feet x 660 feet. Its typical streets are also 132 feet wide.
This is because of Gunter's chain. These are 10-chain x 10-chain blocks and 2-chain streets.
The same is true of other cities. Looking on the other end of the spectrum, Portland's compact street grid is comprised of blocks that measure 198 feet x 198 feet. These are, in other words, 3-chain blocks. Its typical streets are also 33 feet wide. So half-chain streets.
Units of measurement have a lasting way of influencing how we plan and design things. This is true at small scales and it's also true of our cities. In tomorrow's post, we'll look more closely at Salt Lake City's street grid and what it does to walkability.
A couple of years ago, an architect friend of mine from Chicago (who was in town for work) told me that when it comes to units of measurement the building industry in Toronto is schizophrenic. She basically said, sometimes you use the international system (metres) and sometimes you use customary units (feet).
And this is absolutely the truth. We are constantly switching back and forth between the two. The drawings that go into the city are in metres and millimetres, but the drawings that get shown to prospective renters and buyers are in feet and inches. We’ll say that the Tall Building Design Guidelines stipulate that towers should be 25 metres apart, but then in the next sentence say that we’re going to need a 24 inch transfer slab.
This kind of measurement bilingualism is so common that I bet some of you have cheat sheets with common conversion factors posted up at your desk. It probably includes things like: 1 square metre = 10.76 square feet.
Over the years though, I have found myself naturally drifting more and more towards metres and millimetres. So much so that when people throw out inches in a meeting, I’ll now sometimes ask them what it is in millimetres: “Wait, how thick does the slab need to be?” A lot of this has to do with the fact that all city planning documents are in metres. So it’s simply more efficient to stick with one system of measurement and avoid constantly converting back and forth.
That said, there are still lots of people who prefer feet and inches (particularly in my industry) and many instances where I default to thinking in customary units. I’m 6 foot 3, not 1905 mm. But, I am ready to go all in with the international system. I think it would make life simpler and more efficient. After all, it is called the international system.
What system of measurement do you think in?