St. James Changing of the Guard?

I read about the smaller "changing of the guard" at St. James in the guidebook. But, I am unclear where to stand for the great photo-op referenced. The words in the book say the guards march up the Mall. But the table says they march up the Spur Road (where is that?) to St. James. Rick's book references standing "at the corner" but I'm unclear on which corner. Can anyone help? Thanks!!!