"I come from the city."
Translation:Ab urbe venio.
I've found "ex urbe venire" in an old Latin/French dictionary, with this meaning "coming from the city".
It's not the only dictionary or grammar book where I've found this construction, so it seems okay.
I've also found that "ex urbe" seems to be used often with verb like "to exit":
"Exire ex urbe" in "Oratio in L. Sergium Catilinam Prima".
("Exire ex urbe" maybe like when you have to go out from the city, because there's a threat)
I don't know if there's a difference in intensity between "ab urbe" and "ex urbe".