In addition to the reports, letters, and other textual documents, the The War of the Rebellion: a Compilation of the Official Records of the Union and Confederate Armies includes an atlas containing an extensive set of battlefield maps, illustrations, military campaign plans, and other land surveys corresponding to events spanning the Civil War.
These maps and illustrations were created to support battle reports and correspondence covered in the War of the Rebellion records. They are a wonderful visual resource for studying military operations and campaigns of both the Union and Confederate forces.
You can browse the War of the Rebellion records and locate individual maps and illustrations as they are referenced throughout the text. You can also browse a PDF inventory to locate maps independent of the text. Digitized copies of both the War of the Rebellion records and the accompanying atlas are also available online.

Image: (Above, Left) Map of the Battle of Murfreesborough, Tennessee, December 31, 1862 to January 3, 1863. The War of the Rebellion: A Compilation of the Official Records of the Union and Confederate Armies Atlas: Part 7, Plate 31, No. 1.
Image: (Above) Portion of plate showing Union and Confederate Army uniforms. The War of the Rebellion: A Compilation of the Official Records of the Union and Confederate Armies Atlas: Part 35, Plate 172.