The city is a giant platform powered by giant movable solar panel that tracks the direction of sunlight, also wind power was fully harnessed.
Most cities float around the globe as they will, some float on the ocean.
Some cities float above desert to obtain better sunlight, and it creates a more habitable climate for the area below the platform, desert can be fully inhabited, giving more living space for human. However the population didn't grow exponentially, rather it was well controlled. Instead the population of robots grew ever faster and became an equal specie as human, they gained equal rights, respect and social statues over many years conflict and debate, but it was an inevitable trend, since human pursued to create beings that intellectually equal to human themselves, they must also acknowledge these creatures shall enjoy equal rights as human themselves(as Children are given birth by parents but that doesn't make children a inferior generation than their parents).
