During the Civil War, the Union and Confederate armies developed field offices for their topography operations. This allowed both sides to produce the most accurate and up-to-date maps possible. As they moved further into enemy territory, the Union armies in particularly became depended on these roving map offices. Often, map-makers would have to produce maps on a days notice. This was the case with Sherman's Army of the Cumberland as it sliced through the Deep South in 1864. According to an essay written by Richard W. Stephenson, author of Civil War Maps: An Annotated List of Maps and Atlases in the Library of Congress, Sherman's Army of the Cumberland’s topography department under Col. William E. Merrill produced a series of very accurate and important maps during Sherman's Atlanta Campaign.

This map, according to Stephenson, is a good example of the detail and accuracy of these maps. The map illustrated a passage way through the hilly western edge of the Etowah River close to Resaca, Georgia. The map shows a division of Sherman's army under McPherson camped along Snake Creek Gap, an area according to Van Horn that had not previous been shown on a map (Thomas B. Van Horne, History of the Army of the Cumberland (Cincinnati: Robert Clarke & Co., 1875), vol. 2, p. 457).

For more see Trevor K. Plante's "Enhancing Your Family Tree with Civil War Maps" in the Summer 2003 (Vol. 35, No. 2) issue of Prolouge from the National Archives and Records Administration