Don't forget that Toronto, for instance, is south of Boston. If you fly from Toronto, you will likely have to fly over U.S. airspace to get to other places in Canada exactly because of flying straight lines.

>>How do 40% of flights between Canadian cities encroach on US airspace? Or is that your point? I'm not a flight buff, so I'm think in terms of straight lines of flight, but is that not the case?
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>I was surprised too.
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>But it seems that there are factors like better efficiencies because of jet-stream, improved safety because of more tracking capabilities, and some other stuff.
>Most larger Canadian cities are within 100 miles of the U.S. border. The map shown on the news showed airline routes dipping through the U.S. from both west and east, converging on either Toronto or Montreal.
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>>>But you shouldn't worry, because the U.S. is working hard to secure your airspace! Only a few days ago came the news here that the U.S. is wanting to names of every person on every plane that ventures into U.S. air space. This happens to include some 40% of flights between Canadian cities that have no scheduled landing anywhere in the U.S.