I'm using Java, but the language I'm using here is probably irrelevant.

I'd like to create an economy based on an ancient civilization. I'm not sure how to design it. If I were working on a smaller game, like a copy of "Space Invaders", I'd have no problem structuring it like this.

Game -Main Control Class --Graphics Class --Player Class --Enemy class

I'd pass the graphics class to both the player and enemy class so they could call graphics functions.

I don't understand how I'd do this for larger projects. Do I create a country class that contains a bunch of towns? Do the towns contain a lot building class, most contain classes of people? Do I make a path finding class that the player can access to get around? How exactly do I structure this and pass all these references around?

Thanks.