"this isn't a position a senior officer would have chosen by design."

Oh I agree that the Union positions of the first day may not have been the best place to fight. But on the other hand Union Brig. General John Buford did pick the ground for the fight because of the lay of the land. Gettysburg nor the high ground of Cemetery Ridge behind the town had any military value except as a defensive position.

Gettysburg itself had already been occupied by Confederate Troops only a couple of days before and they had moved on to York, Pa.

So why did Buford choose that place to bring on a battle, if the ground was not good ground?

What purpose was he fighting a delaying action for Reynolds' 1st and Howard XIth Corp to come up. Gen. Meade had already issued orders that Pipe Creek was going to be where he would have his army assembly unless otherwise engaged.

Buford and his Brigade commanders of Devin and Gamble were experienced Cavalrymen who knew the value of terrain and scouting. These men knew what the terrain was like. General John Reynolds agreed with them and he was in command of that wing of Meade's Army and he saw the advantage of fighting on that ground.

From the Union standpoint this was a battle where the men on the scene, Buford and Reynolds, Devin and Gamble, chose the ground to fight on. In choosing to fight there they in fact violated Meade's Pipe Creek Order to assemble in that direction. But Meade had given Reynold's discression to act as he (Reynold's) saw fit.

I don't think they were force by circumstances to do that. They could have withdrawn and not engaged Hill and Heth. There was nothing at Gettysburg for them to defend except Honor.