[bombcar]

It's entirely unreasonable to expect cities to look like some perfect gradient of density like something out of Cities Skylines; you'd expect the central desirable areas to be the most dense, and pockets of density here and there, but you'd still find single family homes even in dense areas for quite awhile. Paris didn't become as dense as it is overnight, and even there you can find relatively low-density housing quite close to the CBD.

The question I'd have is how close is a non single-family dwelling (exclude duplexes, too) - I'm in a relatively low density ruralish town, and there's an apartment building a block away on one side, and three on another.