This early siege map shows relative positions of the Federal Army Corps on June 21, 1864, photoprocessed with annotations. Note the sketchy nature of the basemap. NARA RG77 (see Stevenson, Guide to CW Maps in the National Archives, pg. 48).
H.Q. Army of the Potomac. Detail showing lines opposite Petersburg, scale 4 inches = 1 mile. Confederate lines from June 15-17 are sketched in red.