Smithsonian.com: A Cutting-Edge Second Look at the Battle of Gettysburg

The technological limits of surveillance during the American Civil War dictated that commanders often decided where to deploy their troops based largely on what they could see. Using today’s digital technology to visualize the Gettysburg battlefield, we can better understand what Lee and his commanders could – and could not – see at decisive moments during the battle.

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http://www.smithsonianmag.com/history-archaeology/A-Cutting-Edge-Second-Look-at-the-Battle-of-Gettysburg.html