One very common idea in sci-fi stories is ships or 'dwellings' in outer space. It is impossible to create gravity just with a static platform, but one way you could emulate gravity in space is with the Stanford torus. Ideally, an entire population could live comfortably in an Earth-like setting on the Stanford torus, with gravity and an atmosphere.
The original idea requires the torus to rotate once per minute to provide 0.9-1.0g of artificial gravity (actually centrifugal force). So with roughly 10 rotations per minute, we could create an Earth-like atmosphere.
The problem is that the bigger the torus, the faster it would need to turn to maintain the level of gravity we are used to on Earth. Thus, the builders would need to balance between size and speed, which means we could not build a torus big enough for everyone in the world.
In the far future, all the countries' borders have effectively dissolved, and the whole human population answers to one overarching government. Due to the deteriorating conditions on Earth and the increasing environmental problems, this government has the resources to build just one torus that could provide a good living for 1% of Earth's population. This leaves everyone else 'stranded' on Earth.
In a dystopian society, it would probably be the rich, the powerful and the influential who get to bully their way into a better life away from the troubles of Earth. However, this is (not exactly Utopian) a much fairer society, where the government wants to give everyone a fair chance of getting that better life.
How would the government give everyone a fair chance of getting onto the torus, assuming there is minimal corruption? How would they convince the rest of the world, who are still living on Earth, that the best chance humans have for survival would be to let their relatives or friends live safely and happily in the torus, while rest of them slog it out on a decaying Earth?
Basically, I'm trying to avoid the situation in Elysium, where people are unhappy with the arrangement of the lucky few in the torus, and the rest stuck on Earth. They are fighting to get onto the torus, and the best way I can think of so far to avoid this would be to convince the world that they need to stay on Earth, to allow humans a chance of survival from the Torus. But, obviously, many wouldn't get this, and you'd have those who care only about themselves...
Edit: There was one story called Atlantia, by Ally Condie, where the government managed to convince the majority of the population that they needed to allow the minority to live in a safe haven, while the majority worked to support them from a polluted world. And the majority didn't fight to live in the haven. In that case, the haven was in the sea. However, how the government did that was not really explained.