In order to be considered a city, it has to be dense enough to support a bus network. If no bus, then no city. Sprawling town.

I'm thinking predominantly urban area, probably at least 100k people in a non seasonal capacity. Eg. Pullman Washington is a small rural town that becomes huge during college and quiet in the summer as the students leave.

I tend to think of city limits as the boundaries of a city -- not the broad metropolitan area. Shorline is not Seattle, neither is Bellevue or Renton.

Edit: That said, we used to have streetcar suburbs as a prevailing model. Spokes that radiated out to the suburbs on relatively fast, uncomfortable streetcars. A similar model with trams or BRT could function.