The citi-block is the standard habitat in all Mega Cities. Each one is a towering skyscraper capable of housing 10,000 people.
Each citi-block is also fully stocked with a small weapons arsenal. There are no armies in the Mega Cities, only the Judges, so each block has it's own set of defences in case of invasion. A City-Def squad in each block is trained to act as a small militia, making each block a mini fortress in times of war.
There are occasions when having such an arsenal can cause problems. When 10,000 people occupy one building, allegiance to one's block is everything. Tensions between blocks build to levels of mass hysteria, and the smallest event can trigger full-scale war between neigbouring blocks. If not contained swiftly, thousands of fatalities can be expected. This is known simply as Block War.
The block names were also used as satire, with names such as Leonard Nimoy Block, Esther Rantzen Block, etc....
But that's a whole other node....