As a follow-up to yesterday's post about infill housing and overall urban densities, let's look at some basic math.

The City of Toronto has an estimated population of 3,025,647 (as of June 2023) and a land area of 630 square meters. That means that its average population density is about 4,803 people per km2. Obviously this number will be higher in some locations, and lower in others. But overall, this is the average.

Now let's consider how many people we could actually fit within the existing boundaries of the city (city proper not the metro area) if we were to simply match the average population densities of some other global cities around the world.

Again, what this chart is saying is that if we took the same physical area (Toronto's 630 square meters) and just increased the population density to that of, say, Paris, we would then have a total population of over 13 million people and we'd be housing an additional 10,011,573 humans on the same footprint.

I am not suggesting that this is exactly what should be done. (Though, you all know how much I love Paris.) What I'm suggesting is that calling a place "full" isn't exactly accurate. How would you even measure that? What someone is really saying is that they are content with the status quo in terms of built form and density.

Note: The above population densities were all taken from Wikipedia, except for Toronto's figures, which were taken from here.

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

Phoenix is the 5th largest city in the United States. It has a city proper population of about 1.6 million people and a metro area population of close to 5 million. It is also one of the fastest growing cities in the US.

But being the desert city that it is, its population consumes more water than its natural aquifers can support. Which is why there is something called the Central Arizona Project (CAP).

Approved in 1968, the CAP diverts water from the Colorado River into the state of Arizona. The system is 336 miles (or 541 km) and it runs from Lake Havasu to Tucson, via Phoenix.

Here is an aerial image of the canal from Wikipedia Commons:

And here is a system map from CAP:

Today, it is the single largest water source (and consumer of power) in Arizona, serving about 80% of the state's population. This obviously makes it invaluable. It delivers on average about 1.5 million acre-feet of water per year. (Acre-foot = Acre of area x one foot in depth.)

I was reading about this project today and I found it fascinating. Maybe some of you will too.