We compiled the data on international air travel from the IATA database, supplied by Diio, LLC through their APGdat service [29] . Similar to prior analyses [15, 16, 17, 18] , we used direct connection information with regards to aircraft type and passenger capacity to calculate the connectivity of Mexico with all airports included in the database, and summarized this information (as direct flight capacity) at the country level. Additionally, we estimated the number of connecting passengers (indirect flight capacity) by calculating the number of passengers (p i,j ) arriving at airport j from airport i, and then estimating the number of passengers (p j,k ) going from airport j to airport k, based on all flights reported in the database. We limited the potential connections (trip jRk) to flights that departed no sooner than one hour after the first trip (iRj), and no later than six hours after the arrival of the first trip. We also disallowed return of passengers to Mexico once they left the country, and the return of passengers to North America once they left that region. We thus obtained a quantity, x i,j,k , that estimates the total potential connections to airport k available to passengers from the first trip (iRj). Setting constant the fraction of all passengers that connect (x), we obtained an estimate of the number of passengers with two leg itineraries for each potential destination (iRk; Eq. 1):