https://math.stackexchange.com/quest...le-can/1235083


It doesn’t take a whole lot if cities to generate “hundreds and hundreds of city pairs.”

The pairing calculation involves factorials (N!) which get pretty huge pretty quickly.

It’s sort of like the birthday paradox: if you get only 23 randomly chosen people together the likelihood of two of them having the same birthday (day not year) is about 50%, just because there are such an incredibly large number of pairs you can generate from 23 people.

Hundreds and hundreds of city pairs can rather easily be generated by only a little over a dozen cities. The issue may be more one of demand and how frequently (or infrequently) the flights to some (or all) of those pairings can run and still turn a profit.