1. Bureau of Economic Analysis. http://www.bea.gov/regional/downloadzip.cfm. Bureau of Economic Analysis. http://www.bea.gov/regional/downloadzip.cfm.
2. Bureau of Transportation Statistics. http://www.rita.dot.gov/bts/data_and_statistics/by_mode/airline_and_airports/index.html. Bureau of Transportation Statistics. http://www.rita.dot.gov/bts/data_and_statistics/by_mode/airline_and_airports/index.html.
3. National Transportation Safety Board. http://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx. National Transportation Safety Board. http://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx.
4. U.S. Census Bureau. https://www.census.gov/population/metro/data/. U.S. Census Bureau. https://www.census.gov/population/metro/data/.
5. The role of wealth in the demand for international air travel;Alperovich G.;Journal of Transport Economics and Policy,1994