Originally Posted by https://sampwiki.blast.hk/wiki/SetPlayerWorldBounds

SetPlayerWorldBounds(playerid,Float_max,Float_ min,Float:y_max,Float:y_min);

playerid The player you want to set the boundaries of.
Float_max The max. x-coordinate where the player can go.
Float_min The min. x-coordinate where the player can go.
Float:y_max The max. y-coordinate where the player can go.
Float:y_min The min. y-coordinate where the player can go.
This function does not return a specific value, it's best to simply ignore it.