iZurvive is a map for DayZ and Arma 3 that lets you place tactical markers (player positions, tents, meeting points, etc.) on it and automatically shares those markers with the friends in your group. It's the easiest way to coordinate your team in the huge open world of DayZ and Arma 3.

You can also use the app to find and coordinate your team. Just pick a map and place the markers on it. The app will automatically show you the players in your group who are nearby and who are currently playing. It also shows you the number of players and their positions. It's really easy to use and it's completely free.