The City (都市, Toshi) is a vast cybernetic labyrinth that began its construction on Earth, and is the overall setting of the Blame! universe.
The structure of the City can be best described as a multi-layered Dyson Sphere. It's layout is similar to that of an onion, with a Megastructure forming the border of the layer.
Actual construction appears to have been random and unplanned with the Builders constantly creating passages, buildings, and all kinds of other structures only to take them apart and constantly rebuild again. At one point an entire Megastructure Level was built off the grid and not integrated into the system.