I am currently working on a turn-based 4X game, and one of the things I quickly ran into was a question of scaling. On one hand, I want things like realistic sizes (having some idea of what each tile represents in terms of area), but on the other hand, doing so would limit me in terms of certain mechanics I want to implement (the size of a realistic city would not even occupy a tile, let alone multiple tiles, a mechanic I want to use).

How would I go about scaling the world so that I can have both realistic scaling AND the mechanics I want?

Some things I have considered:

Changing the size of the world. Nothing says that I have to have this take place on an Earth clone (especially with randomly generated terrain). Smaller worlds might allow the detailing I'd need for the cities without having unrealistic tile sizes.

Foregoing the realism: Something that came up while I was researching was that ancient cities were tiny by today's standards. Ancient Rome (the part encompassed by the Aurelian Walls) was only 5.3 square miles (for comparison, Manhattan is 22.96 square miles- enough to fit four Romes). I could forgo the realistic sizes of cities and make them the size I want for my mechanics.

What is the best way to balance realism and mechanics for the scaling of a game world?