During the early morning hours of July 3, 1863, the third day of the Battle of Gettysburg, Confederate General Robert E. Lee issued orders for a massive military assault on Union troops. It proved to be disastrous for the Confederates, forcing Lee to retreat and ultimately abandon his attempt to reach Washington, D.C. through Pennsylvania.
As Rebecca Rosen points out over at The Atlantic, surveillance technology lacked much in the way of aerial capabilities, leaving Lee unaware of just how many Union troops he was attacking on the final two days of battle.
Middlebury professor of geography Anne Kelly Knowles, who has been working on a mapping visualization project about the Civil War's most famous battle, tells Rosen that by exploring the map from Lee's perspective, she discovered that he "could not have known the full extent or formation of the Union troops" when he decided to launch his unsuccessful assault.
However, both the Union and Confederate armies were able to generate maps of the site. And however limited they may have been, the maps helped in the following months and years explain the story of what happened during the battle. The diagrams that showed troop positioning and Gettysburg's geography added an important element to the stories being shared among military officials, troops and civilians. Below, courtesy of the Library of Congress, a look at some of the Battle of Gettysburg maps made during the Civil War: