How does mvsd duel maps work?


I am making a game similar to murder vs sheriff duels (mvsd) and inside mvsd when you join a map that has a open sky, you can’t see other maps in the distance. Only you and your opponents are able to see the map.

I am wondering how was this made?

My guess is once the duel started (from the server) the server sends the client data and the client creates the map for only the people in duel. Therefore only they can see it. I am not sure if this really is the case though. I want to recreate this.