Tier City is a multi-level megastructure constructed during the last days of Old Earth.
Tier City acquired its name due to consisting of multiple levels, or Tiers, numbering into the hundreds. Commuter corridors lead to personal habitation Pods. Residents of Tier City are discouraged from leaving their pods, and it is illegal to use transport outside of Tier City itself.
The residents of Tier City listen to the Network Feed for all of their news, information and entertainment. The most popular programme on the feed is hosted by a shock-jock politician called The Preacher.
Tier City is surrounded by an uninhabitable radiation belt known as The Red Zone.
In Episode 3 Delivery Incoming, Rachel hears an audio file about Insignia Life Enterprises, which mentions a contract for supplying genetically modified foods to the four Tiers, suggesting that there may be more than one Tier City megastructure on New Earth.