For the non-data nerds out there, can you explain why Prince's Island Park and the Stampede grounds are part of "Downtown Calgary"? The rest of the boundaries make intuitive sense to me.
StatsCan assembled the downtown areas out of their existing dissemination areas, which are small areas intended to be consistent through time, compact, follow neighbourhood boundaries, etc. And which have around 400-700 people per DA. Here are DAs in central Calgary:
Basically, they figured out the distribution of employment density in the city, and then picked any DAs that had density at least 40% of the highest density area. (One reason our downtown is relatively small is because it has a high peak of density; if there were fewer jobs in the middle of downtown, we would have a larger downtown.) From this core, they then added a semi-arbitrary* 1 km buffer to capture near-downtown residential areas. But it's built out of the DAs, so the boundaries will follow the DA boundaries.
As I mentioned, StatsCan defines DAs on a population basis, so there are intended to be 400-700 people in a DA. Which is fine in areas that are residential, but breaks down if there's other land uses. Look at Repsol Centre in the figure above; it's in the same DA as most of Erlton (north of 25th/26th ave). And it also has the cemeteries. And a bunch of industrial. And... more residential in Parkhill, down to 42nd Avenue. Does this make sense? It has 400-700 people in it, so that's all StatsCan cares about. So non-residential lands tend to get lumped in arbitrarily with nearby residential use; the Stampede is in the same area as the residential around the Elbow River Casino, Prince's Island is in with some Eau Claire residential. If the residential is in, the non-residential follows.
The final cut after all of their hard work trying to find downtowns that are consistent based on objective criteria across Canada was then running the geography past local governments, which I suspect is the other reason Calgary's downtown is so small. The north boundary is the river, but there are DAs in Sunnyside that are 1 km from the Courts Centre, which surely is in the high-density employment core. Much of Lower Mount Royal is in the 1 km buffer of Western Canadian Place, again, presumably in the high-density core. There are a number of DAs in lower Crescent Heights that are within 1 km of The Bow. The downtown that Statistics Canada uses is nearly identical to the Centre City policy area, used to determine a bunch of City policies (like why the cycle tracks on 5th St dead end at 17th Ave, the imaginary Centre City boundary, rather than going down to the Elbow River like makes sense). I suspect that Calgary told StatsCan that Centre City is our downtown, and to use the DAs that make up Center City as best as possible. (The Stampede is in the Beltline Community, therefore in Centre City).
I did my own attempt to replicate StatsCan's work. The DAs I chose as the employment core are in green based on the employment data I had, which is not the same as StatsCan but is probably fairly comparable. The blue is the 1 km buffer around the employment core, and the yellow DAs are the selected ones -- it excludes the Stampede (and the SW corner of the Beltline at 14th St/17th Ave. But it includes a good chunk of Sunnyside and Kensington, of lower Crescent Heights, Lower Mount Royal and Cliff Bungalow.
So I'm 90% sure that the City told StatsCan to make our downtown a fair bit smaller. My estimate is that there's roughly net 11,000 people (in 2016) in the area that is in the downtown on StatsCan criteria but not in the official definition. Going from 39K (in the official version) to 50K would mean Calgary had a larger downtown population than Winnipeg, Hamilton and Victoria in 2016 and we would probably have passed Edmonton in 2021.
* They were basing their work of a US Census analysis that added a 1 mile buffer for the same reason. They used 1 km because this is Canada and we use metric, I suppose. They try to justify it in the paper by saying that most people walking to work in 25 minutes or less, which is right, and that a 25 minute walk is roughly 1 km, which is wrong -- that assumes people barely walk at 2 km/h. Google uses 4.8 km/h in giving their directions; the standard I've generally seen used in Canadian transportation planning is 4 km/h. 25 minutes walk at 4 km/h is... 1.67 km, or almost exactly 1 mile. Also, they use straight line buffers because they lack basic GIS competence.