The pilot district. Part 1 first shows it through a public optic-conduit that carries footage of the Concourse; it is where the Correction hits Renee in Chapter 1 and where R.S. later walks a district rebuilt 'to stop negotiating'. The book says it is reached from the Spire by transit membrane, has a primary pedestrian concourse, a plaza with a bio-ceramic fountain and a Carbon Void tower beside a pedestrian bridge, and Part 2 calls it the first place the Failsafe is applied.
From the books
“The image was from a public optic-conduit in Sector Four.”
Part 1, Chapter 2: The Frame That Won't Stay Gone, p. 28
“A localized cluster near the Sector Four pedestrian bridge.”
Part 1, Chapter 3: Calibration Drift, p. 52
“If something survived a direct wipe, moved across districts, and resisted averaging, it wasn’t just a glitch.”
Part 1, Chapter 5: Public Safety, p. 107
“Sever connection to Sector Four hardware cache.”
Part 1, Chapter 6: The First Thread, p. 135
