Your question suggests that a city begins with one center and the evolves into two or more centers. I would think to the contrary that nearby cities exist and grow into a two or more center city. Examples include Champaign-Urbana, Illinois and Dallas-Ft. Worth, Texas.

Thanks a lot for your answer. That is the case for some American cities, but I think that many Chinese cities are not developing in that way. Anyway, your comment shows a different and important perspective on this issue.