What constitutes the "missing middle"?

[hipster duck]

I think there's a lifestyle preference for inner city, walkable living to people who advocate for the 'missing middle'.

When people talk about how Toronto or Vancouver are just made up of single family homes and high rise condos/apartments, they're generalizing a lot but, beyond that, they're focusing strictly on the walkable, inner city parts of those metro regions. On the outskirts, missing middle is the majority of what they build: semis, townhouses, and low rise multifamily.

If all parts of the region were equally valuable and desirable, there would be less of an argument for MM, since it's already supplied, it's just not geographically well distributed.