Harper's Ferry is a genuinely strategic place. It sits at the confluence of two rivers, the Potomac and the Shenandoah. The town also had an important arsenal there, meaning a stockpile of rifle-muskets and the machinery needed to produce them. Harper's Ferry is also a gap in the blue ridge and the top of the Shenandoah valley, a rich agricultural area.

In contrast, Frederick and Gettysburg were not really very important places, they were crossroads towns that happened to be on the line of march once or twice. If the Gettysburg campaign had an objective apart from forcing a battle with the northern army itself, it might be said to be the railroad line that ran from Philadelphia via Harrisberg to Pittsburg and points west. This would have been a moderate inconvenience to the Union if occupied or temporarily damaged.