The map is used for navigation around Chernarus. It is most commonly found in supermarkets, but has a chance to spawn in all residential and military loot spawns. The added functionality and ease of use of the DayZDB map makes this item largely unnecessary.
The map does however remain useful when coupled with the GPS as it can be used to find your current location based on a grid reference, and is the preferred method of navigation by certain players who feel that the use of out-of-game tools makes their game experience less immersive and enjoyable.
On recruit difficulty servers, and some regular difficulty, maps will allow you to see your own location as a blue dot marked "Survivor" and also any vehicles you are inside. If you have just left a vehicle, it will remain on the map for about a minute before disappearing but nobody else can see it. You cannot see the location of other players unless they have just left a vehicle you were inside. This feature makes the GPS a useless piece of equipment as you can already see your location with the map, and in a much more convenient manner.