This doesn't always work, the Greater Toronto Area (GTA), even if you take the most narrow interpretation, is made up of a bunch of different transit systems. Walking along on Google Streetview, there is no way you could tell when on Yonge Street you have "left Toronto", and need to pay extra fare on TTC, or take YRT/Viva/Blue etc.

But it's a neat idea to think about transit and accessibility. I'd love to know at which point in the world you can reach the most people within an hour of transit for example, or two hours... This is the advantage in the Pearl River Delta (and probably Tokyo) - there is tons of high-speed rail, subways etc, so you can probably reach about 40 million within 1.5 hr (an hour high speed rail and half an hour on local transit). Whereas it takes me an hour and a half just getting to the airport in Toronto.

I like this. The next step down must surely be the Super City. In New Zealand the Auckland "Super City" would love to be a mega city. Auckland's fragmented and disconnected transport system, chaotic local government arrangements and expensive attempts at integration make it substantially less than a megacity. That and the low population count.

Oh I like that definition. Means that you'd count the Gold Coast and Brisbane (and Ipswich) together as a megacity, which is kinda true, as "South East QLD".

The GVRD renamed itself to the Metro-Vancouver about 5 or 6 years ago. The Vancouver Metro area is the exact same thing as the GVRD. They aren't different things.

I don't like this, because it means the Bay Area will likely never be considered a megacity :(