Arcis is a city surrounded by a border wall. Important locations within the city include Ash's house, the sewers, the subway and aboveground tracks, the Authorities' base and warehouses, the skyscraper graveyard district, the construction site, the power plant, the border wall, and the factories.
The city was the only habitable place for miles, as far as [Ash] knew. According to the Authorities, it was an island in the middle of a toxic wasteland. All around the city was a huge landscape of trash, hazardous chemicals, and many other dangerous substances. She had never seen it, because of the border wall, but it was what everyone was told was out there. A few people had tried to escape, but most were hunted down and killed before they even reached the border wall. No one had ever managed to escape from the city, and no one got past the border wall. It was impossible to escape—alive, at least.
“By my design, the vast majority of the surviving millions were living in the city of Arcis. I had allowed only a few small-scale bombs to reach there. After I made a show of using my armed forces to stop the fighting across the globe, I arrived at Arcis with legions of my soldiers and engineers to proclaim peace and begin the process of transporting the survivors to a gleaming new city I had been building in secret. I left a small population of workers in Arcis to run the remaining factories there."