Hengsha

Heng Sha is densely-populated island off the coast of Shanghai, on which a second street level has been built above ground level. It is at the heart of the global augmentation industry.

Plot
Jonathan Jacques-Belletête, Human Revolution's art director, has said:

Shanghai's Heng Sha is a lot more into the trans-humanist thing. It's a lot more accepted there - it's the Silicon Valley of all cybernetics. Within the art direction everything that's more like that is more golden, and a lot more towards the cyber-renaissance. The dual layer is inspired by a mockumentary we saw quite a while ago, which appeared to be a real documentary about Hong Kong... In the game the idea isn't that it's the poor at the bottom and the rich at the top; the bottom used to be the Mecca of cybernetics, a lot of the headquarters of the great labs and manufacturing plants are there, it's just that when they built above it they chose a different architectural direction. So above they have new universities and new headquarters, but the bottom isn't a slum - there isn't an old school dichotomy. We put a lot of stuff in the game, like you'll see those student-types from the upper level coming downstairs at night to party, and hit the bars and brothels.

Trivia
The dual-layer principle was also used in Seattle in Invisible War. There, a rich-poor divide was very much in effect.