The midway point is basically the 404. That means East York, Scarborough, Markham, all of Durham, and points East. Comprising roughly 1/4'th of the population of the GTAH. Doing the same for Hamilton gives a midway point of Bronte. Placing only Burlington, and Hamilton as GTA municipalities that are closer to YHM than YYZ, or roughly only 1 million people. Yes there are other cities (K-W, Guelph, the entire south shore of Lake Ontario/the Golden horseshoe, Brantford, London, etc), however there is also lots of cannibalization in the region as there are 3 airports operating in that region (Hamilton, Waterloo, and London). I think if we are gong to make the argument for 3 regional airports serving a catchment area of ~3 million+ people (on top of a major international airport in YYZ, and competition from Buffalo), than the figures don't look as bad for the East end. There is literally no international airport with scheduled service East of YYZ until you get to Ottawa.(~450 km away)