Although fictional, I'd like to think that Grand Valley is located somewhere along the Canadian Rockies, perhaps near the coast. Seems like a speedway slicing through the lush, mountainous topography with deep water-filled ravines would be something you may find in North America. That's what I imagine, at least.
ERacer
See, i always thought Grand Valley is over in France.
Matter of fact, i formed my opinions early in gT1 & 2
Deep Forest: south Germany. Because in GT1 & 2, German flags are featured most prominently in the grandstands. Also, Deep Forest is used in the European Nationals of GT2.
Apricot Hill: I used to think England, but now i imagine somewhere in East Europe....basically where Apricots grow famously. In GT4, those tall mountains in the background also give us a clue.
Midfield: Japan. Again, Midfield was featured in the Japanese Regionals and Nationals in GT2.
Route 5: Vancuover, Canada....Route 5 passes thru Vancouver in real-life. It also passes thru many American cities; however, some of the terms on those billboards are in metric, so it can't be in America...we use miles instead of km.
Route 11: Somewhere in Japan.
Trail Mountain: i used to think over in England because this track gets featured (again) in GT2's European Nationals & Regionals. But now i'm not sure. I dont have an opinion....they don't have large, craggy mountains in England, do they?
An arborist could study the trees & foliage at this track in GT4 and give a more conclusive opinion. ...also there's that monkey in the tree at turn # 7. Monkeys don't typically sit in trees in England.
Autumn Ring: Somewhere in west Pennsylvania where the Appalachian mountains are. Or it could be Kentucky or West Virginia. I'm biased cuz it looks like areas where i grew up.
Driving Park/ Motorland tracks: Ohio. It's very flat. But this could also be California, Japan..many places. the scenery is very common.
Test Course: Again, this could be anywhere with flat, boring scenery. I prefer to think sometimes it's in Japan, and sometimes in California. Sometimes in Europe. There are testing tracks like this huge oval all over the world.
Complex String (GT3): I prefer to think Japan for no reason other than they got some crazy car-testing tracks (like Twin Ring Motegi) and to me, CS is nothing but a big test track. No races are actually held here in GT3 sim-mode if i remember correct.
Super Speedway (GT2 & GT3, not Twin Ring Superspeedway in GT4): California for sure. This is a NASCAR-style track with the banked turns and such. In GT3 there are huge electicity-generating wind-turbines off-track, which are commonly seen in Cali.
Red Rock Speedway (GT2): Arizona. Lots of iron-rich rocks out there. Could be Colorado, too, near the Red Rock Amphitheatre. Or is that New Mexico. I forget.
High Speed Ring: Japan. Looks like Fuji. Looks like the track in Pole Postion from years ago. I'm voting for Japan.