in vienna people usually greet each other in the same building, even if they don't know each other. could be that is only true for me as I greet everyone and maybe they just do it back.
Ya maybe it's a U.S thing idk. I make a point of being as friendly as possible, and live exactly where I do in kind of the more low-key former streetcar suburb area with bars and such around, so that I can shout to friends if I see them on the opposite side of the street