Just discussing the " limited" vs " unlimited" attribute related to space/expansions, as someone stated first and another asked what he/she meant. Last night, at my most advanced city, I unlocked/placed the 950K medals expansion and there are no more medals or diamonds expansions available for me.Again, t here is no unlimited space available. Good, that will only means a new limit will be defined. Lets think that some time in the future, before a new age is released, the developers modify the expansion area grid to enlarge it to accommodate 16?, 20? or X? more expansions. The expansion grid area do not grow with eras. But, sooner or later the current expansion grid area shown around the city will be full. Yes, they can keep adding new eras or parts of an era, and with new era/part of an era they will likely continue adding new Victory (Medals) expansion, additional reward expansions at Map / Research Tree, two (2) more diamonds expansions. The expansion grid area also has a limit.There is a limit to the total expansions you can unlock.
For every type of expansion, there is an individual limit of expansions available to unlock.