This is the map of Santa Carla. It is taken from the tablet in survival mode but the basic location is the same with story mode.

House shape icons are the safe houses.
Small pink circles are the place where you can find figures for new cloth.
White hammer icon is the craft machines that you craft new items and weapons.

U (with yellow mark house) is the main house for the host player In survival mode
O (with pink mark house) is the guest house for the first guest join the session
M is the base camp (for most of the weapons)
B is the diner
P is the hotel
W is the grave yard.

You can find 4 magazines of explosive bullet in the house in B (for XM8 rifle), in the safe house in W (for M9 beretta pistol)