Let's continue with our theme of city blocks and talk about another city with a noteworthy street grid: Barcelona. Up until the middle of the 19th century, Barcelona was a tiny medieval city hemmed in by 6 km of walls and totalling just over 2 square kilometers. If you look at a map of the city today, it's pretty easy to see where this was:
This was of course done for military purposes. Barcelona's medieval walls helped the city resist siege after siege. But the result was also overcrowding, unsanitary conditions, and a generally low life expectancy. So after much debate, it was eventually decided that the walls would need to come down and that the city would need to expand outward.
This then raised the question: how should it be done?
Enter a civil engineer named Ildefons Cerdà. Created in 1860, the Cerdá Plan for Barcelona was a continuous grid of blocks intended to guide the future growth of the city, similar to what the Commissioners' Plan did for Manhattan. The blocks measured exactly 113.3 by 113.3 meters and each was to have a central open space of at least 800 square meters.
In his original plan, the streets were to be 35 meters wide. But supposedly these were narrowed to no more than 20 to 30 meters due to criticism from the public. Wide streets and more lanes were, I guess, not seen as a benefit in the second half of the 19th century. Either this, or landowners simply wanted bigger buildings.
The Cerdá Plan got approved in 1860 and, today, the city looks like this:
One particularly unique feature of this plan was that the blocks all had/have chamfered corners. This improved visibility at the intersections, as well as created opportunities for public spaces and other uses. For better or for worse, today, you'll find parking for cars and scooters, bike share stations, ramps leading to underground garages, patios, and more.
The heights of the buildings on each block were also intended to be capped at a consistent height. But even with relatively few tall buildings, the Cerdà Plan led to one of the densest cities in Europe. Today, it is also viewed as a highly livable and desirable city. Hence why the city announced a total ban on short-term rentals. Too popular.
Now for a comparison. Last week we spoke about Salt Lake City's large city blocks (here and here). And so for fun, here's what these blocks would look like on top of Barcelona:
The most obvious takeaway is that Salt Lake City has larger city blocks than Barcelona, and that's one reason why, objectively, Barcelona is more walkable and urban than SLC. But I think you could also view this graphic as a tremendous opportunity.
Barcelona is in the midst of rethinking its urban fabric around something called "superblocks." The idea here is to cluster blocks together and then concentrate transit and vehicular traffic along its edges, creating a more pedestrian-focused center. For example, in its largest form, a superblock might be a 3 x 3 grid, creating a grouping of 9 city blocks.
But it doesn't necessarily need to be a 3 x 3 grid. Other permutations are possible and the city plans to eventually introduce over 500 of them.
The first superblock was implemented in 2017 and, not surprisingly, it improved air quality, increased quietness, and led to a significant decrease in car usage (-92%). Interestingly enough, it only led to a moderate increase in car traffic on surrounding streets (+3%). Traffic can be a funny thing.
Creating superblocks out of smaller blocks is naturally easier than the opposite. You have an existing grid to work with. But there's no reason that the opposite can't also be done. And I think that's one way to look at Salt Lake City's street grid. It already has its superblocks. Now it's just a question of creating all of its smaller blocks.
Conventional planning wisdom tells us that smaller city blocks are generally preferable to larger city blocks. They make for more interesting walks (which can change our perception of distance) and they improve overall connectivity. This is why you'll often hear planners advocate for things like "mid-block connections." It is a way of creating the feeling of smaller blocks.
Salt Lake City, as we have talked about, is the opposite of this. Its blocks measure 660 feet x 660 feet (call it 200m x 200m for those of us more accustomed to using the international standard for measuring things). This means that if you were to walk only 2 blocks (inclusive of 2 streets), your walk would be close to 500m, which is a commonly used walking/transit radius.
Things get a bit tricker when you're not walking in a straight line. For example, if you found yourself wanting to cross a street somewhere in the middle of a block -- and you wanted to obey all traffic safety rules and not jaywalk -- you would need to walk over 200m just to get to the opposite side. So basically a whole other block.
There are also instances where even this street grid gets interrupted. This past weekend, I spent an evening walking to and from dinner on Main Street. And at one point, I got caught trying to cross the convention center (which occupies 3 blocks). I guess I could have tried to cut through, but I walked around, which added 2 additional blocks (~600m in total).
Thankfully, SLC also has many instances of new mid-block streets/connections, road diets, internal laneways, and enhanced center medians, among many other things. I mean, here are some plans to turn Main Street into a pedestrian promenade. All of these interventions are an effort to soften the city's underlying block structure, which we know tends to be indelible in cities.
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.