After the Earth's resources were exhausted, the humans, in dire need of help, made a deal with the Company to settle Mars. After that planet was depleted, the Usurians moved the humans to Pluto. To this end the planet was terraformed with an atmosphere, and a city which the Doctor found quite impressive, Megropolis One. Later five more Megropolises were constructed. Each Megropolis was lighted by one of six artificial suns, in the form of fusion satellites. At the end, the planet housed 300 million humans.
Megropolis One was the main administrative centre, where the Collector administered the operation through human underlings from his palace. Other cities were Megropolis Three, which housed miners, and Megropolis Four. All Megropolises had extensive industrial capacity.
As a side-effect of the perpetual day caused by the artificial suns, many inhabitants were afraid of the dark. The monetary unit was the talmar.
Humans in the colony were ruthlessly exploited. They were drugged through the air with a substance called PCM, making them subservient. Furthermore they were taxed extensively, with tax evasion or simply being unable to pay the high fees a grave crime. Criminal offences were curbed through screening with an extensive surveillance system, and caught criminals were deported to a detention centre in Megropolis One, where they usually did not survive very long. A more severe form of punishment was execution by steamer, often public.
A freer society of outlaws existed in the undercity though, where PCM was not distributed and people were able to think more freely. They eventually managed to sabotage the PCM dispersion system in Megracity one, which led to a successful uprising against the company. Once the company retreated, declaring their branch to be no longer profitable, the humans intended to re-settle the Earth, which the Doctor thought to have been regenerated. (TV: The Sun Makers)