There is a lot of fun to be had considering the cases for passenger airlines in the US, since the large traditional hub-and-spoke airlines all maintain multiple

There is a lot of fun to be had considering the cases for passenger airlines in the US, since the large traditional hub-and-spoke airlines all maintain multiple hubs (in fact, following the most recent round of merger consolidation, each of the big three US airlines has at least seven hubs in the country). That's a multi-way tradeoff between local population and desirability as a destination (to ensure plenty of profit-making opportunities on direct flights); proximity to other important destinations (to offer short connections to non-hub cities); coastal or northern locations (good for trans-oceanic or long great-circle routes); climate (to ensure your hub doesn't get frequently shut down by adverse weather); congestion (to ensure your hub isn't frequently delayed by the sheer amount of traffic to coordinate); airport layout (to give you maximum efficiency for lots of flights); etc., etc. When people wonder, for example, why Atlanta is consistently the busiest or second-busiest airport despite not being an obvious first-tier American city (those being New York, Chicago and Los Angeles), the weather, the congestion and the airport layout are huge factors. Atlanta doesn't get a ton of snow or severe thunderstorms like the northeast or upper midwest, it isn't in an overloaded air corridor like the northeast, and the airport's runway and taxiway configuration allow multiple simultaneous takeoffs and landings with much more ease than someplace like O'Hare (which is basically beyond capacity at this point with its configuration).