Thanks for sending me the UK link. Looks like a online library for works on world cities but not very user friendly-looks like a site from the 1990's. Updated site but not really easy to see anything.

Is there a real definition of tier cities or opinions? This link just gives random guesses from people. Link to Quora Looks from your comment that the tier system is only opioions.

As for Sacramento International Airport, it's not that busy but only 100 mile drive to San Francisco International Airport. Link to Sacramento International Airport Land price would be cheaper in Sacramento than San Fransico and a short drive to the airport of 100 miles could save Amazon a good amount of money.