We summarized these connections at the country scale, thereby estimating connectivity for nearly every country on the globe with Mexico through either direct or indirect flights; the only countries excluded would require an overnight stay in a hub airport, or three or more connecting flights. We validated our algorithm (eq. 1) for connections within the contintental U.S.A. (the only data on actual itineraries, including connecting flight information, to which we had access). We randomly chose 50 connecting itineraries within the U.S.A. and compared our predictions to the actual routes. Our predictions were statistically significant, using a simple proportional model with log-normal errors, and explained over 60% of the variance in actual routes (F = 83.71, p,0.001 on 1, 49 d.f, adjusted R 2 = 0.6232).