Originally Posted by
beachmouse
Since different states set different annexation and municipal consolidation rules for urban core city populations, it's best to use metro area size estimates 2018:
Atlanta 5.8 million
Boston 4.6 million
Detroit 4.2 million (add in adjacent areas like Ann Arbor and Windsor and you go over 5 million)
Seattle 3.7 million
MSP- 3.2 million
Charlotte 2.4 million
Cincinnati- 2.1 million
Salt Lake City- 1,2 million
And for cities with only one large airport, the combined statistical area (CSA) actually gives a better view of the catchment area. For most places, this is actually a small change (for example, Atlanta's only grows +14% to 6.6M through the inclusion of, e.g., Athens, GA), but some can be quite large - Seattle's CSA is 1M people larger at 4.7M (+27%). Salt Lake City is actually the most extreme example of this - it goes from 1.2M for the Salt Lake City metro to 2.3M (+92%) for the CSA (it includes places like Ogden and Provo which are both less than an hour drive from SLC). Charlotte sees a very, very small increase (+8%) to 2.6M (from 2.4M for the metro area alone).
In general, in places with only one large airport, people will drive to the nearby "large" airport. For example, people in Athens, GA and Ogden, UT definitely drive to ATL and SLC respectively (both Athens Regional and Ogden don't have any real commercial service for example). Even for places with multiple airports (e.g., think SFO CSA which includes San Jose) - people will often drive an extra hour if needed for a nonstop or for a better deal.