SimCity 2013 limits the maximum size of a city to approximately the size of a “medium sized SC4 city.” There has been lots of discussion on whether these size limits are too small.
On one hand, some argue that the region-based game play works better if each city is small and focused on a particular task:
My second observation is that the size restriction forces specialization. If my city were three times bigger, it could eventually become a coal mining college town with a great tourism and gambling industry. Having an omnicity may not be especially fun. It would lack focus, and because cities interact with others in a region, we won’t need every city to be everything.
I personally feel that the “cities are too small” complaint has some merit. Real cities need to be able to facilitate a large number of different demographics and requirements. Part of the challenge in previous SimCity games (and real life, for that matter) is juggling those requirements to create a city which depends on its mining and resources industry, but is also heavily residential with some tourism thrown in. Such a scenario will create interesting conflicts between the needs of various citizens; making the game more interesting and challenging.
With a bit of luck; we’ll see the size restrictions alleviated in a future patch or expansion pack.