Toronto and Chicago density comparison

 Chicago is a city that Torontonians often measure themselves up to. They're the two biggest Great Lakes cities, and while Chicago used to be much bigger, the gap between them is shrinking.

This is how their urban areas changed from 1950 to 2010.

The density distribution in 1950 was not hugely different, although Toronto peaked at a bit lower densities than Chicago and was more strongly negatively skewed with very few census tracts above 50,000 ppsm (19,000/km2) while Chicago still had a fair bit living at such densities (639,001 people to be precise).

The biggest difference though is probably that Chicago was much bigger, with 4 times the population. This means that population living above any density threshold was much greater.

 From 1950 to 2010, Chicago experienced significant population and density loss in the city proper, part of that was decreasing household sizes, although some neighbourhoods including what was the densest area in 1950 (South Side) experienced abandonment too. The increase in the number of people living at 10-25,000 ppsm was likely largely a result of de-densification of many in-city neighbourhoods. Most of the growth was fairly low density.

In Toronto, the vast majority of growth was less dense than the 1950 average, but still considerably denser than Chicago's growth. The population living at higher densities (25-50k ppsm / 10-18k /km2) remained relatively constant while the population living at very high densities increased, and about half of that was outside Old Toronto. Toronto grew quite a bit more than Chicago too, quintupling its population compared to a doubling for Chicago.

The result is that Toronto and Chicago have a comparable amount of dense census tracts, despite Chicago's urban area still being close to twice the size. This can also be evidenced by the fact that the city propers now have comparable populations and land areas.

Chicago has considerably more low density suburbia. About 30% of the urban area lives in <3,000 ppsm (1200 p/km2) census tracts, compared to less than 5% for Toronto. In Toronto, most of these very low density census tracts contain particular large non-residential areas (parks, industrial, etc). The typical Chicago suburbia is comparable to Toronto's lower density suburbs, while the average Toronto suburb is more comparable to the lower density half of Chicago's pre-1950 development. Brampton, Mississauga, North York, Scarborough and Etobicoke all have weighted densities above 10,000 ppsm (3800 p/km2), are predominantly post-WWII and make up over half of Toronto's urban area population.

Since Toronto is a smaller city, the overall weighted density is higher.




Stats
 
Chicago 1950
Population: 4,562,208
Area: 450 sq mi     (1,164 km2)
Standard Density: 10,149 ppsm      (3,918 p/km2)
Weighted Density: 27,099 ppsm     (10,463 p/km2)

Population over 20,000 ppsm: 2,593,494      (7,772 p/km2)
Population over 10,000 ppsm: 3,520,152      (3,861 p/km2)

Toronto 1951
Population: 1,088,515
Urban Area: 112 sq mi      (289 km2)
Standard Density: 9,742 ppsm      (3,761 p/km2)
Weighted Density: 21,337 ppsm      (8,238 p/km2)

Population over 20,000 ppsm: 585,667     (7,772 p/km2)
Population over 10,000 ppsm: 842,973     (3,861 p/km2)

Chicago 2010
Population: 8,944,424
Urban Area: 3,458 sq mi     (8,956 km2)
Standard Density*:  2,587 ppsm     (999 p/km2)
Weighted Density: 9,047 ppsm     (3,493 p/km2)

Population over 20,000 ppsm: 1,120,257      (7,772 p/km2)
Population over 10,000 ppsm: 2,594,751      (3,861 p/km2)
   
Toronto 2011
Population: 5,178,773
Urban Area: 911 sq mi      (2,360 km2)
Standard Density*:  5,684 ppsm      (2,195 p/km2)
Weighted Density: 14,853 ppsm      (5,735 p/km2)

Population over 20,000 ppsm: 993,659     (7,772 p/km2)
Population over 10,000 ppsm: 2,871,565     (3,861 p/km2)

*Urban areas are defined by dissemination area for Canada and I think census block (or block group) in the US rather than census tracts. These numbers are based on all census tracts that are at least partially contained within the urban area. So some of them will include non-urban land, bringing down the density compared to the numbers you might be used to.