Density Terrain

Flickrist neb has a great cluster of geo related photos from the Venice Biennale centered around this gem showing the relative population density for parts of Barcelona:

Now just imagine that the heights are actually tied to density sensors in the field, so that over the course of the day, the relationships change, the heights shift, the mass of humanity migrating around the city becomes it's own datavizmorph. Then imagine a feedback loop, where each barrio has some kind of beacon that gets brighter with the increase of temporal density, people could 'play' the lights of the city by aggregating themselves into certain hoods.