Currently, the biggest limiting factor on city size seems to be access to food - e.g. reaching level 5 seems to require the ability to reach 2 food tiles.

This leads to the largest cities typically being inland, where it is easier to find 2 food tiles within reach of a city center.  This seems to run counter to most of history, certainly in the ages when this game is set, that the largest cities were found near water, where fishing and trade was easier.

I would suggest that a dynamic that would provide incentive to create cities near water would create a more realistic map.  Some choices seem to be:

- trade benefits from being on the ocean or river (harbors come with trade benefits, for instance)

- food benefits (e.g. fishing as a form of "food tile")

- water as a research needed to expand (a new building type - e.g. "aqueduct" - could be added to allow inland cities to get enough water to grow over time)