ACT 1 -18 Total locations
ACT 2 -27 Total locations
ACT 3 -12 Total locations
ACT 4 -15 Total locations
When you get to the point at the end of act 3 (chapter 15) where you have the choice to leave and go to the prison make sure you have 57 total locations. If you only have 56 or less go back and search until you find the one(s) you've missed. For me I was stuck at 44 in Act 2 (knowing I needed 45 locations) and could not find my last location. The Act with the double listing of the gasstation so i quit out restarted my system and bam 45 locations. Not sure if the patch adds a location to fix the double gasstation listing for Act 2 but I then had 45 locations and moved on. So before you search everywhere check you current locations found quit out and reload see if it adds another location for you. But I think it only does this once you reach act 2 since the gas station is listed twice.
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Ok if you seem to be stuck at 71/72 locations and cannot find your last location here is a list of few places to check.
1. First it might be in the City of Moresby. After reading through most of the comments it seems a lot of gamers have missed this spot so... Load up from chapter 15 or your current save that gives you access to the City of Moresby anything after Act II. Check your map and if the bottom left corner (SW corner) of moresby is green this is probably your last location. There is a boat there and you are brought here from a side quest that is miss-able.
2. In Act I part of the main quest you are sent to the inside of the Hotel where you will get a bunch of locations note you can only get these locations once if you return it's blocked. If you do this quest with other players it is possible to miss one or two locations so make sure you do this solo and check these locations off as you see them.
Parking_Zone_Server Room
Parking_Zone_Ambulatory
Parking_Zone_Pool
Parking_Zone_Office Lobby
Parking_Zone_Control Room
Parking_Zone_Parking Ground Zero
Parking_Zone_Kitchen
3. The other place where you could possibly miss a location or two is in the prison ACT IV (if you play solo you will NOT miss any locations). When playing Act IV with other players there is a possibility that you could miss a location if the other players get ahead of you. So to avoid missing any locations here just play solo or stick with the other players.
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List of all locations (not in any order since everyone plays different)
Act1_Zone_DiamondBeach
Act1_Zone_DiamondDistrict
Act1_Zone_GasStationLighthouse
Act1_Zone_GoldenBeach
Act1_Zone_GoldenDistrict
Act1_Zone_Hotel
Act1_Zone_HotelBungalows
Act1_Zone_GasStationTunnel
Act1_Zone_SilverDistrict
Parking_Zone_ServerRoom
Parking_Zone_Ambulatory
Parking_Zone_Pool
Parking_Zone_OfficeLobby
Parking_Zone_ControlRoom
Parking_Zone_ParkingGroundZero
Parking_Zone_Kitchen
Act1_Zone_OldMarina
Act1_Zone_OldMarinaWorkshop
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Act2A_Zone_CanaleStreet
Act2A_Zone_Graveyard
Act2A_Zone_Church
Act2A_Zone_DeadZone
Act2A_Zone_DownTown
Act2A_Zone_EasternWaterfront
*Act2A_Zone_GasStation
*Act2A_Zone_GasStation?
Act2A_Zone_MarketDistrict
Act2A_Zone_NicksHub
Act2A_Zone_OldTown
Act2A_Zone_OldtownBridge
Act2A_Zone_PoliceStation
Act2A_Zone_Riverside
Act2A_Zone_ShantyTown
Act2A_Zone_SimonsHub
Act2A_Zone_VictoryHill
Act2A_Zone_Warehouses
Act2A_Zone_WastewaterPlant
Act2A_Zone_WaterfrontHarbour
Act2A_Zone_WesternWaterfront
Act2A_PumpFactory_Name
Act2B_Zone_TownSquare
PoliceStation_Zone_Station
PoliceStation_Zone_Parking
PoliceStation_Zone_DetectivesOffice_Name
PoliceStation_Zone_ChiefOffice_Name
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Act3A_Zone_GaiaFalls
Act3A_Zone_Mowen
Act3A_Zone_SmugglersMarina
Act3A_Zone_GhostTown
Act3A_Zone_JungleVillage
Act3A_Zone_OverpassCamp
Act3A_Zone_RiverVillage
Act3A_Zone_SmugglersCamp
Act3A_Zone_Waterfall
Act3B_Zone_Laboratory
Act3B_Zone_LabWorkshop
Act3B_Zone_NativesCamp
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Act4B_Zone_Basement
Act4B_Zone_CB0Armory
Act4B_Zone_CB0Canteen
Act4B_Zone_CB0Enternance
Act4B_Zone_CB0FirstFloor
Act4B_Zone_CB0Kitchen
Act4B_Zone_CB0SecondFloor
Act4B_Zone_CB0Warehouse
Act4B_Zone_CBA
Act4B_Zone_CBB
Act4B_Zone_CBBControlRoom
Act4B_Zone_CBC
Act4B_Zone_CBCMainRoom
Act4B_Zone_Hospital
Act4B_Zone_Sewers