There are 8 locations in the game but they are not available in just one discipline:
Here are the 8 locations and what season they appear in the Dirt Tour:
Finland (Rally and Trailblazer) Season 1
Kenya (Rally and Trailblazer) Season 1
Michigan (Rally and Trailblazer) Season 2
Norway (Rally and Trailblazer) Season 2
Aspen (Rallycross, Landrush and Head2Head Season 1
L.A. Coliseum (Rallycross and Gymkhana) Season 2
Monaco (Rallycross, Gymkhana and Head2Head) Season 2
Smelter (Rallycross, Landrush and Head2Head) Season 1
You need to win one race at each of the locations, you can unlock this by winning online races (Thanks to K0RNMA5T3S for confirming), Dirt tour events and Single Player races.
If you go through the Dirt Tour this will unlock at the end of season 2.