The Kawasaki Locker map is a specific treasure map in Dragon Quest IX. It is named for the location where it was initially distributed and shared via Tag Mode by the player who randomly received it. Like the Masayuki map, the map acheived massive popularity in Japan.
The Locker map is famous for the high amounts of very rare treasure chests it contains. In particular, it contains 4 tier S and 6 tier A chests, greatly increasing a player's chances of receiving very rare items. For more info on the map's contents, and a full map, see here (Warning! Site is Japanese). Best used in conjunction with this.