The annual economics meetings will take place in January 2015 in Boston. Today I booked tickets for my wife and myself from LA to Boston. There are very few direct flights (especially non red-eye) flights connecting these cities. In contrast, United has plenty of direct flights from San Francisco to Boston (I see seven on January 2nd). Doesn't this suggest that there is more trade between San Fran and Boston than between LA and Boston? Why would that be?
A city is a bundle of industries and tourist attractions. San Fran is the high tech mecca and so is Boston. Los Angeles is trying to do high tech but is off to a slow start and LA's high tech seeks to complement the entertainment industry. The programming and science skills of the nerds at MIT and Harvard may not be a good match with the sleek beauty of the LA set. So, I'm not surprised that there are so few flights between LA and Boston. Expected demand may affect the willingness to supply flights!
I have tried to use Google Scholar and I can't find serious papers using city to city airplane visits as a measure of "closeness" of industries. Almost 20 years ago, Ed Glaeser's Harvard student
Takuo Imagawa studied a slightly related issue. Google Scholar is not helping me to track down his thesis.