7 regions
Belknap is the volcanic region south of the Cascade, home to Ada Tucker's Hot Springs camp and the town of Marion Forks. You come here early for Tucker's work and stay for its seven Hordes and three infestations.
Cascade is the northern starting region, in the Farewell wilderness around Copeland's Camp at Peaceful Lake. It is where you learn the game, and it still has 8 Hordes and 4 NERO research sites to come back for.
Crater Lake is the far southern region built around the real lake and Wizard Island, the Militia's headquarters. It opens in the second half of the story and has the most encampment jobs and NERO research sites in the game.
Highway 97 is the southern stretch of US highway running through Chemult and past Chemult Community College. It has more Hordes than any other region, including the 300-strong Lobert Draw Ridge Horde, so bring your best gear.
Iron Butte is the Rippers' home territory in the east, locked until late in the story. Come here for its 11 R.I.P. Sermons, two Ripper ambush camps, the Rogue Tunnel checkpoint and the Cloverdale research facility.
Lost Lake is the central region of the map, built around a resort lake that holds Iron Mike's Camp. It becomes your main base for the middle of the story and packs 6 Hordes, 3 infestations and Sherman's Camp.
Pinnacles is a cut region east of Highway 97. You cannot enter it; both ways in are blocked. Data miners found plans for a sixth camp, Fort Klamath, ranches and farms there, plus a cut Act 4 mission.
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Bunkers
Bunkers are underground shelters hidden at most ambush camps. Clear the camp and open the hatch to get a bed, a save point and a locker. Many also give a crafting recipe and a regional map.
Farewell
Farewell is the Oregon city where Deacon, Sarah and the Mongrels lived before the outbreak. It falls at the very start of the story and only appears in flashbacks, so you never ride its streets in free roam.
Pinnacles Camp
Pinnacles Camp is a cut survivor camp from the removed Pinnacles region, near Crater Lake. It would have been the sixth encampment, and you cannot visit it in the released game.