I have understood that urbs is not just a "city", but more properly a "major city". The L&S entry implies that it refers to a walled town, but city walls are rare nowadays. What makes a city an urbs in the modern world?
Recently, when answering a question, I referred to New York as urbs (to distinguish the city from the state). I think I would call New York an urbs, but it got me wondering about the word. Where would you draw the line?
I understand that there is not going to be a hard definition, but some examples, counterexamples, or other insights would be illuminating. I am not looking for a list of all urbes, but a rule of thumb. Is it just a matter of size, or do cultural or administrative considerations enter the picture? Or should I just call whatever would be a "city" in English an urbs in Latin?