smaller communities exist in big cities too. They might be neighbourhoods like a small town, or interest, cause or activity-based. The trick is not to defer to government to provide them for you, which I think is harder in big centers.
Harkening back to the GP post: Mr. Rogers Neighborhood was based on a city neighborhood, not a small town.
Seasame Street, as well.
This is very true - some apartment buildings have great community (of course, plenty don’t). Demographics certainly drive part of the distinction, but just having a person step up and do the barest amount of leadership is also critical.