A map of Chernarus can be found as Loot ingame which then can be accessed using the M key by default. Maps are one of the most sought after items in the game. They don't use up usual Inventory slots, but go into the tool slots below the sidearm slots. However, they use 1 inventory slot when stored in the backpack.
Maps can be used as a waypointing system by holding shift and clicking a location, making them useful for navigation. They may also be used to mark destinations by double clicking a location.