This is part of The Last Agent DLC.
There are a total of 20 Survivors that will need to be rescued; 5 in each area. If a surivor dies, they will not respawn and make this achievement impossible to get. It's best to go for them as soon as you begin this DLC. The Survivors are as follows:
South Almuda: Jack, Mila, Maia, Vicki, Ryan.
Central: Madeline, Bob, Sam, Alec, Jordan.
Sunset Hills: Eva, Greta, Alex, Jasmine, Tracey.
Ingleton: Steven, Kristen, Mike, Scott, Kaliyan.