Pittsburgh by day
So for Pittsburgh, the latest estimate of the city's daytime population is calculated to be 457,049 or more than 48% above the resident (or presumably nighttime) population. The report is really just looking at flows of commuters to work, and not other potential reasons the daytime population is likely higher than the resident population. Add in the number of folks coming into the city for school, shopping, business or for most any service including inpatient and outpatient hospital services, and for sure the 'daytime' population for the city of Pittsburgh is much higher. I'm pretty sure that if we took the time to add up some of those other factors we can get over the 500K number I think people like to quote... or make up depending.
What is really more noteworthy is that this is not just something typical of other cities. Pittsburgh ranks pretty high compared to all other places in terms of how big a percentage 'surge' of people come into the city each day. When ranked against other large cities Pittsburgh continues to have one of the biggest daytime 'surges.' By my ranking (among the 100 largest 'plaxces') only DC, Atlanta, Orlando, Miami and Paradise, Nevada have larger % increases (I'll post some benchmarking later..) . Paradise is really part of Las Vegas and DC is arguably an artificial concentration of government jobs. So Pittsburgh comes pretty close to the top. If only we had Disney World here to get us past Orlando....
Actually what is worth noting is the trend. The first link there is from a 2006 story which looked back on older data which calculated Pittsburgh's 'daytime' surge to be +41%. So we are not getting an estimated +48% surge likely reflecting the decline in population over the decade coupled with the stability in the number of jobs.
Pittsburgh's high ranking is a function of our fragmentation locally and how small the city of Pittsburgh is within the labor shed. Also the remarkable number of jobs that have remained concentrated within the center city. Again as I've mentioned before: The City of Pittsburgh has a nearly identical number of jobs located within the city proper as it did over a half century ago if not further in the past. So population decline for sure, but whenever anyone says the number of 'jobs' in the city has gone down in either the long term or even the short term, ask them what they are referencing.
When you consider the population was a lot bigger back then it must be that that a big chunk of those jobs were retail and service sector jobs directly tied to the resident population. For the job count to have remained the same, despite the big loss in resident population, there must have been significant growth in jobs that provide goods or services to the world outside of Pittsburgh.