Hi! I'm programming an engine which creates complete cities for a realtime application. The Problem is, that one sees most of the time the complete city from the air - but it's possible to zoom in and go between the buildings too - so it must look good in both situations! I'm using LOD for the geometry and the shaders... But i really worry about Texturememory! Mipmapping won't help me on that... Could you give me any hints or tips or anything that comes into your mind to that topic? Thanks!

How close up do you want players to be able to see the city?

You might check out how Civ4 handled it. I remember reading a couple of articles about how they implemented it (Might have been on Gamasutra)

Why can't you use custom LOD on the texture too?

Have certain boundaries or distances where the current texture set is unloaded, and a new set loaded in. Obviously, as you get nearer you need much higher res textures, but you also need less of them, as you can see less.

You can still use mip-mapping on the textures loaded to help with the image quality.

Hope that gives you a few ideas
Spree