I have installed hardword floors in my dinning room and stairs. I am now reading to take on the upstairs hallway. However, I am not sure which wall to start from. The hallway is basically U-shaped with an open railing overlooking the stairwell. At the base of the railing is a pine board. I want the hardwood floor to be flush against the pine base. I am unsure which wall to start from. Thanks.

Go diagonal then you can start any place you want.

start on the pine nosing base...butt up against it..then back fill the other areas...

depends on which way your joists are running, i didnt see the direction on the drawing.
In any case I would start off the pine base of the stair railings.
If you start off the pine base along the bottom of the drawing and work towards the wall, when you reverse the area for the nosing it will be set up for a piece os spline, the other side id nail that backwards (right to left) to get nice and tight to the pine base.

Joists run up and down (vertical) as viewed in the drawing. I did not think of using splines to reverse the directions. I think I will start at the pine base of the railing. Thanks