Though limited, these sketches help explain what happened, and why.

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. 

What Gettysburg looks like today. View Larger Map

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:

"Gettysburg battlefield" 1863. Confederate positions hand colored in red. "Shows troops and artillery points, drainage, roads, railroads, dwellings with names of occupants, several points of interest on the battlefield, and a few of the highest points by hachures." Courtesy Library of Congress.
"Gettysburg battle-field. Battle fought at Gettysburg, Pa., July 1st, 2d & 3d, 1863 by the Federal and Confederate armies, commanded respectively by Genl. G. G. Meade and Genl. Robert E. Lee" 1863. "The locations of the corps, divisions, brigades, etc. of both armies, with the names of commanding officers, are given in detail. Badge symbols are used to identify the Federal corps." Courtesy Library of Congress
"Gettysburg Third day. Position of troops" 1863 to 1865. Color coding indicates the location of Union and Confederate forces. Courtesy Library of Congress.
"Plan of the Gettysburg battle ground" 1864. "Map gives Union positions in black and Confederate positions in red, batteries and lines of fire, roads and streets, vegetation, drainage, and relief by hachures." Courtesy Library of Congress.
"Map of the battlefield of Gettysburg" 1864. Courtesy Library of Congress.
"Copy of official plan of Gettysburg. Pennsylvania, fought 1st, 2nd, 3rd July 1863" 1862 to 1865. "Drawn by R.K. Sneden, 40th NY, Hdqs. 3rd Corps, from plan furnished by Genl. D. B. Birney, Color coding indicates the location of Union and Confederate forces." Courtesy Library of Congress.
"Union army's march on Gettysburg from Frederick, Md." 1863 to 1865. "Plan showing the concentrated march of the Union army on Gettysburg, Pa., from Frederick City Md., June 30th and July 1st 1863." Color coding indicating the location of Union forces.  Regional view shows paths taken by different segments of the Union army on a march from Frederick, Md., to Gettysburg, Pa., as well as the location of the Confederate army units in the vicinity. The Union troops were under the commands of Reynolds, Howard, Sickles, Slocum, Hancock, Sykes and Gregg. Courtesy Library of Congress.

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