Supertown, also known as the Celestial City, is the capital of New Genesis and home of the New Gods. It was built by Highfather and Atinai to be the ultimate civilization where Gods could come to realize their true potential. Although many live there, the planet's surface is inhabited by another group named the Primitives who choose not to leave the untamed wilderness.
The DC Universe heavily changed its continuity into the DCnU following the events of Flashpoint in 2011. This was part of an effort to make storylines more accessible to newer readers, beginning with the New 52. This new timeline combines elements from the DCU, Vertigo Universe and Wildstorm Universe while drastically changing the origins and histories of characters.
After the Multiverse's rebirth, the floating city that orbits the home-planet of the New Gods is New Genesis itself.
Their original world, Genesis, was ravaged and left inhospitable by the first war between the brothers Highfather and Darkseid, thus the surviving New Gods took to the sky and have remained there since then.
Even after the planet's nature returned and it's life once again restored, they choose not to return and leave their world in ruins in order to remind themselves of their previous mistakes, with Orion claiming they can possibly return once "they prove they're worthy".
On the Earth-designation-51, which harbors an "aspect" of the New Gods, the Genesisians reside in their celestial home of Supertown atop the Screaming Mountains were they can only observe and indirectly influence all the events on the world, most notably the exploits of the last boy on Earth Kamandi.