I generally said hi to people in a ~50k pop city, and would regularly recognize people by face even if I'd never spoken to them before. Certainly in the ~1.5k village I grew up in you'd know most people, again if not their names, and would always say hi.
But in that city there were still multiple "centers" - the local pub, couple of shops and whatever - Being the European style town that was actually like 15 different villages that slowly merged. Perhaps because of this it really acted as multiple smaller towns in many ways.
There's probably quite a big variation based on local culture, density and other things, but I'm pretty sure it's a trend by size.
But in that city there were still multiple "centers" - the local pub, couple of shops and whatever - Being the European style town that was actually like 15 different villages that slowly merged. Perhaps because of this it really acted as multiple smaller towns in many ways.
There's probably quite a big variation based on local culture, density and other things, but I'm pretty sure it's a trend by size.