Hi 13oojum, yes it's just a screenshot that is now nearly 7 years old. At the time the game had only just been released and no one had put a full map up so I figured I would share this. I also started writing a guide that I never finished that had more information but in both cases the devs kept updating the game so it became a pointless chore. There is a wiki online that has up to date information :)

This map doesn't show the "precise location|" of survivors, nor is it annotated. It's just a screen.

Thanks iiyama, the map was copied from the original release of the game so is over 2 years old now. I'd be very surprised if it's still correct especially since the game has been updated since. I've been thinking about replaying it, maybe this is my opportunity :)

believe you are missing church encampment (about midway down on far east side)

Some areas only show up once you've been explicitly told about them - the farm north west of the shelter is one. You get it after an encounter at the start of day 40 something I believe.