This solution includes:
1) Basic Info
2) How to Find Your Stats
3) Quickly Finding Them on the Map
4) Upgrades and Fast Travelling
5) Data Stations Quick Link
1) It will take around 2-3.5 hours depending on how many you picked up during story mode etc. The numbers for each region are:
-East Coast 31
-The South 53
-Mountain States 39
-West Coast 53
2) To find your stats you need to activate a landmark (newly discovered or not) and press square to 'toggle display' this will show you how many you have found in each area.
3) To find those last few remaining landmarks; Open the map >> put your courser over empty space >> press square to show filters menu >> press R1 to the exploration tab >> landmarks to undiscovered >> data station to undiscovered >> hidden car to discovered >> zoom out enough to see all states >> turn the right stick in all directions until it snaps onto a landmark.
4) An annoying part of this trophy is getting over difficult terrain, up mountains, over rivers etc. Fast travelling can make this a lot less frustrating so max out "The New World" perk for a bigger discovery radius and just fast travel when you need to.
5) Finding all data stations will make finding landmarks much easier, they all appear on the map from the start of the game but one is hard to find in the mountain states because it blends in with the white terrain, It's at 5:40 in this video TrueAchievements
Feel free to comment any suggestions