These maps should go in the maps folder inside your StarCraft II folder (Default SC2 location is C:\Program Files (x86)\StarCraft II\ on Windows). If there is not a "maps" folder there already, you must create it, and put the maps there.
Note for linux users: the folder name is case sensitive.
This map is different to the Flat48 map found in the Blizzard repos because it changes the map from being a 4 player spawn map instead to a 2 player spawn map.