Arcology

Arcology, combining "architecture" and "ecology",[1] is a set of architectural design principles aimed toward the design of enormous habitats (hyperstructures) of extremely high human population density. These largely hypothetical structures would contain a variety of residential, commercial, and agricultural facilities and minimize individual human environmental impact. They are often portrayed as self-contained or economically self-sufficient.

The concept has been primarily popularized, and the term itself coined, by architect Paolo Soleri,

Archologies or Mega Structures are a actually quite rare and only common on a few of the Union Core Worlds such as Blue Moon,? Attika Station? and Pluribus Unum, where real estate is of enormous value and population desnity exceeds the available space.

Overpopulation is a non existent problem and the Union activley encourages increased birth rates as there are countless planets and worlds to colonize.

Of course technically the Mega and Gigamon space stations are Archologies of sort.