I don't take credit for this guide so I'm posting the link below. I found this guide more helpful and used it for the achievement.
https://steamcommunity.com/sharedfiles/filedetails/?id=46227...I will repost the guide from the steam page if you prefer to stay on TA. The guide on Steam also includes additional map images if you find that more helpful.
First thing you need to know is that you need to see the actual red text appear in the bottom-left of the screen for the location to count. Some places like the Gas Station and Oldtown Bridge may be a bit awkward to get the text to pop up. Keep dancing around an area until you find that succulent sweet spot to make it pop.
There are only 71 actual locations in the game. The gas station in Moresby is a weird buggy thing and counts twice. To get it to count twice, once you've been to the gas station and it has counted once, quit out and then reload your game. Your achievement tracker will have gone up by one more location.
You need 57 locations before going to the prison (Act IV). There are 15 locations at the prison that can easily be found by doing all of the quests. Do all of the quests the prisoners give you and you'll find every location in the prison.
I've listed a lot of locations below as "Unmissable." Obviously this is assuming that you yourself do the quests and complete the story. Don't let co-op partners run through quests without you. Missing one location will be a huge pain later when you have to check every location again.
Green on your maps means you haven't explored there yet. As a point of reference, when you've gotten all of the locations in Moresby, there should be pretty much no green left anywhere in the city, and the west and south coasts will not be green. There will still be quite a bit of green left on the Jungle map, and some on the Resort map. These two maps have much fewer locations, all of which are pretty straightforward, so follow the guide below to check them.
Big thanks to Necrophage33 and DarkoScannley... and all the nice ladies in my life.
Act 1
Resort
1. Golden Beach - You will go through here on your way to the Lifeguard Tower.
2. Hotel Bungalows - Your story quest marker will take you through this location on your way to the hotel. These are on the south side of the Hotel.
3. Golden District - You will go through here during the first Lighthouse story and side quests.
4. Silver District - You will go through here during the first Lighthouse story and side quests.
5. Diamond Beach - North east corner of the beach. The Resort Bunker 2 fast travel location is on Diamond Beach
6. Diamond District - These are the bungalows east of the Resort Bunker 2 fast travel location. The side quest "Family Matters" will take you here.
7. Lighthouse Gas Station - This is the first gas station you go to, when getting a can of gas for Mike at the lifeguard tower. You will also get your first box of juicepacks here.
8. Hotel - Unmissable. The story will take you here.
9. Old Marina Workshop - Unmissable. The story will take you here. This is where the mechanic works on your truck.
10. Old Marina - Unmissable. The story will take you here. This is the area surrounding the workshop above.
11. Tunnel Gas Station - This is the gas station in the south west corner of the map. You will go here for your second box of juicepacks.
Hotel
12. Office Lobby - Unmissable. The story will take you here.
13. Kitchen - The story will take you here.
14. Pool - The story will take you here.
15. Ambulatory - This is where you collect the morphine for Ken. It's possible for a co-op partner to run here and get it without you, so make sure you follow.
16. Control Room - The story will take you here. This is where you talk to Mike Davis.
17. Server Room - The story will take you through here. Just make sure you don't let your co-op partners run in and reboot all the servers without you.
18. Parking Garage - The story will take you through here. Just make sure you don't let a co-op partner run in and get in the truck (which initiates the cutscene and ends the Hotel area) before you enter the parking garage at the end of the Hotel map.
Act 2
Moresby
To be sure you get all of the locations in Moresby, do every side quest, and make sure your co-op partner doesn't complete a quest without you present. The following quests will take you through quite a bit of the city: "Message to the Masses," "The First/Second/Third Head of Cerberus," "Last Chance On The Wall," and "A Voice From the Sky." Also, there is a quest given you to by a man in the southwest section of the city where he tells you his daughter has been kidnapped and asks you to rescue her. This side quest will take you to a fenced-in warehouse that is a location.
19. Church - Unmissable. The story will take you here.
20. Graveyard - Just outside of the church is an obvious graveyard.
21. Victory Hill - Southeast of the church/graveyard, in the northeast corner of the map. You'll pass this on your way from the Church to the Warehouse when doing the quest to hang posters.
22. Supermarket District - South of Victory hill, and northeast of the Warehouse. Again, you'll pass this on your way from the Church to the Warehouse when doing the quest to hang posters.
23. Simon's Hub - This is the Warehouse fast travel location. Doing the quest to hang the posters around town will take you here (first poster location).
24. Nick's Hub - This is Abandoned House safehouse/fast travel location in the very south of the map.
25. Police Station - The side quest to hang the posters will take you right past the police station. You'll know when you're there because you'll hear them speaking through the speakers to you, saying they've taken the police station. You'll also go past here on your way to the pumping station. This is in the northwestern area of the map.
26. Gas Station - Unmissable. The story will take you here. **See Section 1 about counting this location twice.
27. Canal Street - Not far north of the gas station, running through the quarantine zone. The Third Head of Cerberus side quest will take you here.
28. Quarantine (Dead Zone) - Just west of the Warehouse is the quarantine zone. You'll have to climb a ladder to enter. It'll be marked with biohazard symbols on tall walls, and when you get in, you'll notice white tents set up.
29. Downtown - The northwest corner of the map, just northeast of the pumping station. This is where Stan Dart asks you to clear out his house.
30. Eastern Waterfront - The very southeastern corner of the map.
31. Old Town - Southwestern area of the city. The area just southeast of the pumping station. This is the area where you find Yang Chi and he asks you to rescue his daughter.
32. Old Town Bridge - Just north of the pumping station is a big broken bridge with a ton of busted up cars parked all over it. To get the actual word to pop up can be hard - I had luck with the alley that heads to the south from to the bridge.
33. Riverside - The very south of the map, there's a boat on the coast. The beach around this boat is the location. This is just south of the fenced in warehouse in the south-southwest you'll be going to for a side quest.
34. Shanty Town - Southeastern area of the map. The quest "Message to the Masses" will take you here. It's where you meet Garrett Grant.
35. Warehouses - This is close to the very south of the map, slightly west of center. It is a fenced in area that you will go to for a side quest where Yang Chi asks you to rescue his kidnapped daughter.
36. Wastewater Plant - This is where Joseph will lead you as part of the main story quest, when you enter the sewers for the first time.
37. Waterfront Harbor - This is the harbor just north of the pumping station. You will go here in chapter 15 as part of the story quest.
38. Western Waterfront - South of the Pumping Station that you go to as part of the main story quest. Walk southbound along the beach and you'll get it.
39. Pump Factory - This is the "pumping station" that the main story quest will take you to, on the very west side of the map.
40. Gas Station **This is the duplicate counter** See Section 1 for getting this to count as a second location. I found it really awkward to get the text to actually show up. I had to jump on a dumpster from the area to the west and then enter the Gas Station's zone.
City Hall
41. Town Square - Unmissable. The story will take you here.
Police Station
42. Parking - Unmissable. The story will take you here.
43. Station - The story will take you through here.
44. Detective's Offices - The story will take you through here.
45. Chief's Office - The story will take you through here.
Act 3
Jungle
46. Gaia Falls - The story quest going through the Jungle when you enter for the first time will take you through this location. This is where you jump out of the car and escort Jin on foot.
47. River Village - Unmissable. Your first jungle story quest will come from this location. South central of the map.
48. Ghost Town - The first story quest given to you in the River Village will take you through the Ghost Town after Afran's goons. This is just north of the River Village.
49. Waterfall - This is just north of the Ghost Town. You will know if you've been here because it will show up as a fast travel option, called Jungle Waterfall Bunker. It is directly between the Ghost Town and Jungle Village.
50. Jungle Village - Just north of the Jungle Waterfall Bunker fast travel location. Go north up the steep hill, climb the ladder at the top, and head north uphill through the wooden fence. Also, a side quest given at the Overpass Camp to retrieve a camera will take you to the Jungle Village. It is ESE of the Overpass Camp.
51. Overpass Camp - In the very north of the Jungle, slightly west of center. From the Travel to Resort portal in the northwest, go east and you'll see 5 houses on your map just north of the wide broken road. This is the village.
52. Smuggler's Camp - Unmissable. The story quest to Kill Afran will take you here. Southeastern corner of the map.
53. Smuggler's Marina - Unmissable. The story quest to Kill Afran will take you here. Southeastern corner of the map.
54. Mowen's Hut - Unmissable. The story will take you here on Afran's boat. Southwestern corner of the map.
Labs
55. Laboratory - Unmissable. You will go here as part of the main story.
56. Lab Workshop - Unmissable. The necessary lab side quests will take you here. This is the workshop east-northeast of the big lab building.
57. Native's Camp - Unmissable. The story quests will take you here.
Act 4
Prison
There are 15 locations in the prison that are unmissable if you do every quest given by the prisoners.
58. Canteen
59. Entrance
60.First Floor
61. Cell Block A
62. Armory
63. Second Floor
64. Warehouse
65. Kitchen
66. Basement
67. Cell Block B
68. Control Room
69. Sewers
70. Cell Block C
71. Main Room
72. Hospital