> (PS if anyone has good references for images that deal with what
> a city might look like after nan - let me know)
Once nanotech is cheap and common, I would image that 90% of what is now done with above-ground construction will move underground. You get cheap temperature control, cheap materials, and you save the scarce 2-d surface area for things that are valuable there. Earth moving and waterproofing won't be problems anymore; boring through the earth for communication and transportation infrastructure will be cheap (and the most energy-efficient fast transport will be bullet trains in tubes sloped to give gravity-assisted takeoff and deceleration). All you want above ground is parks, farms, solar arrays, dams, and short-distance surface transportation.
A "city", then, would be mostly parks with recreation facilities, gardens, campsites, and a few open-air businesses like restaurants, airstrips (hangars, parking lots, and terminal facilities go under too), auditoriums, beach concessions, etc. No need for "downtown" with big buildings and crowded streets at all, because that's just under your feet, as deep as needed to support the population.