Why "US" in map name when it is in Yukon?

Hi all, I just wonder what the "us" stand for in the map names you see on PTS (us_04)? Is it just me who thinks firstly on the US of A?

It's just an internal naming, behind the scenes all maps and trucks have different file names from what is displayed in the game. In PTS you can see some of them before they get replaced.