The Gnome's Lair has come up with another article on designing cities in games. This one focuses on how to imply size and complexity. The Gnome is currently designing a city for Frogware's The Sinking City.
More information.
Let's imagine for a moment that you have created a unique, believable, sprawling, and impressively detailed metropolis. You have it mapped out, thoroughly described, and have its architectural styles all sorted out. It's a unique, beautiful, and complex place, and you are rightfully proud of it. Only problem is that realizing all of it on screen would probably cost you a few million dollars/euros/pounds/what-have-yous.
Assuming you are neither Blizzard nor Rockstar, you'll thus have to try and keep things as simple and cheap as possible -- your ability to create assets will always be limited. Chances are you will have to abstract and generalize your world, decide to move to 2D, avoid creating an open-world, or to even allow exploration and gameplay in only a handful of locations. As you will not be able to show the full size and complexity of your work, your city, you will simply have to imply it.
Now, take a look at the picture above if you will. Notice how few buildings are actually shown, and ask yourself whether this could be a village scene. Or even a picture taken in a small town.
It could not. Of course, it could not. You know, possibly without exactly knowing why, that this is a picture depicting a part of a big city neighborhood; most probably of a 20th century metropolis. You might only be able to see a tiny part of said city, but this sort of density, and this kind of spatial organization couldn't be found anywhere outside a big urban centre. A town or village would neither be able to support it, nor would they need it.
What's more, said picture provides the viewer with even more information. Information that goes beyond the type of urban agglomeration we are looking at, and lets us feel the living texture of the particular place. A thousand little stories, some of them possible only in this particular city, have left their mark on the hanging clothes, those buildings, the women, and even the wires we see, while the organization of everyday life itself and the class-based nature of those tenements is instantly obvious.
