These are a set of diagrams taken from a recent WSJ article talking about how, "the pandemic changed where Americans live." I know that this is a topic that gets a lot of air time (both here on the blog and elsewhere), but these diagrams do a good job of showing the flow of people, as well as how things may have changed/accelerated since 2018.

These diagrams also remind me of the work of Charles Joseph Minard. A French civil engineer, Minard is best known for his contributions to the field of information graphics, and in particular his flow maps. His most famous piece of work -- which I happen to have hanging at home -- is his depiction of Napoleon's losses during the Russian campaign of 1812.

The map itself is from 1869 and is packed full of information. It shows the number of Napoleonic troops as they left for Moscow, the distance they traveled, the outside temperature (the French weren't properly prepared for the cold), latitude and longitude, the direction of travel, and the location of the troops relative to specific dates.

The point of the diagram was really to show how disastrous this campaign was for Napoleon. The thick beige band on the left is showing over 400,000 troops setting out. But by the time they reached Moscow -- which, by the way, had been abandoned before their arrival -- only about 100,000 troops were left.

The thin black bar on the bottom is showing how many troops ultimately remained and returned at the end of the campaign -- the number was only about 10,000. So the vast majority of Napoleon's troops perished. Supposedly over half either starved or froze to death.

Some 150 years later, and we are still using flow charts to clearly depict the movement of people and things.

The work of John Snow is instrumental to the field of epidemiology. In the mid-19th century, during what was the third major outbreak of cholera, he created the following map showing the clusters of cholera cases in London's Soho neighborhood. Stacked rectangles were used to indicate the number of cholera cases in a particular location. This was a major breakthrough for the fight against cholera because, at the time, it wasn't clear what was causing it. According to Wikipedia, there were two main competing theories. There was the miasma theory, which posited that cholera was caused by bad particles in the air. And there was the germ theory, which posited that cholera could be passed along through food and/or water.

By mapping the clusters of cases, Snow discovered a concentration of incidents in around the intersection of Broad Street and Cambridge Street (now Lexington Street) where a water pump was located that drew water from the Thames. This led Snow to the conclusion that it was maybe a bad idea to offer up polluted river water as drinking water. And sure enough, when the pump was shut off and residents were directed to other nearby pumps, the incidences of cholera began to decline. The germ theory had proven to be true.

The first time I saw John Snow's map was in architecture school. Perhaps many of you have seen it as well. It is often used to illustrate the potential of visual representations to not only tell a story, but to teach the creator what that story actually is. In hindsight, it may seem obvious that polluted river water is something that we maybe shouldn't drink, but it wasn't at the time. This map helped people understand that. Today, we have far more sophisticated tools available to us, but we still have a lot to learn and we're doing that every day -- particularly during a pandemic.

One other thing worth mentioning is that there are a few exceptions to Snow's findings. Supposedly, many of the workers in a nearby brewery were able to completely avoid the cholera infection during the outbreak by only drinking their own brew. Some say it is because the brewery had its own water source, whereas others say it is because the brewing process -- the water is boiled -- kills the cholera bacteria. Either way, I think the moral of this story is pretty clear: when in doubt, choose beer over water.

Map: Wikipedia

Earlier this week I stumbled upon this entertaining article from the Guardian talking about how expensive housing is in London. The author’s tongue-in-cheek suggestion was to setup a new miniature London in the middle of nowhere where everyone could flock for affordable housing, but where many of London’s attributes could be exported: “We can all refuse to wear socks and sell each other overpriced cocktails in jam jars.”

All joking aside, the article is yet another reminder that big global cities are expensive places to live. And in these cities, one of the most precious commodities is, quite simply, personal space. That’s why a garage in London can sell for £550,000 and why a 35 square foot storage cage in New York can sell for $75,000. 

But affordable housing is not the reason why people want to live in places like London and New York. If it were, they wouldn’t be coming. Instead, they come for lifestyle, wealth creation, and the dating market – among other things. However, at a certain point, usually when they form families and start to need/want more space, they start looking around.

Here’s an infographic via the Atlantic showing how relationship status impacts where people tend to live in London. The purple areas indicate an “above average concentration” of a particular relationship status. As you can see, single people tend to live in the core of the city, and when they get married, they move out to the periphery. Intuitively, this probably makes sense to you.

However, I’m always curious as to whether this trend happens more because of consumer preference (people don’t want to raise kids downtown) or because of economic necessity (they can’t afford anything beyond a shoe box apartment). Because if it is largely out of economic necessity (and the Guardian article would suggest it is), then we’re not creating the inclusive cities and neighborhoods that all city builders like to talk about.

So how do we get better at this?

In my view, and I’ve argued this before, the first step should be about improving supply. That is: get more housing built. And the way to start doing that is to make land available and improve the approvals process for new developments. In a recent McKinsey report, they referred to my first point as “unlocking land.”

“Land cost often is the single biggest factor in improving the economics of affordable housing development. It is not uncommon for land costs to exceed 40 percent of total property prices, and in some large cities, land can be as much as 80 percent of property cost.”

The reason this is important is because most big cities operate with massive supply deficits. There simply isn’t enough housing. And so if you can address that at a fundamental level, you can actually do a lot to start improving affordability.