Quarantine zones are the walled, military-run safe areas FEDRA set up across the United States after martial law was declared. Most have since fallen to infection, revolt or abandonment. Boston's North End zone is the one you live in and play through at the start of Part I, and you pass the dead zones of Pittsburgh and Salt Lake City later.
Soldiers scan residents for infection, ration food against ration cards and draft adults into work details. A curfew runs from 6 PM to 6 AM, and the walls are backed by guard towers and a wide patrolled strip outside. Increased checkpoints aim to stop the Fireflies gaining ground, and outbreaks inside are played down.
You start in Boston's zone in The Quarantine Zone chapter, cross the abandoned Pittsburgh zone in Pittsburgh, and walk past the empty Salt Lake City zone and its triage tents in Bus Depot, where Joel remarks on finding yet another abandoned QZ.
The Fireflies, who want a democratic government back, have led uprisings against the military. Pittsburgh's revolt drove the soldiers out but left the city to the hunters, while Salt Lake City became a Firefly foothold for about ten years.
Mission Hill Pier
Mission Hill Pier is the wharf in the Boston slums where the smuggler Robert runs his trade. Joel and Tess fight through Robert's men here at the end of The Slums section of The Quarantine Zone, then chase him through the area.
Boston slums
The Boston slums, marked Area 5 on military maps, are the poor district of the Boston quarantine zone where the smugglers run an open black market. You walk through them in The Slums section of The Quarantine Zone while hunting the smuggler Robert.
Massachusetts State House
The Massachusetts State House, usually called the Capitol Building in the game, is where Marlene sends Joel and Tess to hand Ellie to a waiting Firefly group. It is the goal of The Outskirts and gives the chapter's last section its name.
Austin
Austin, Texas is where The Last of Us Part I begins: the Prologue of Hometown plays out on outbreak night in September 2013 as Joel, his daughter Sarah and his brother Tommy try to escape the city. It is the only region you visit before the 20-year time skip.