and the movements of the army between that river and Mine Run
, in November and December, 1863, had furnished considerable information concerning that region.
The latter experience had proved that the existing maps of the country to be traversed were valueless for the purposes of marching and fighting an army.
The country was of the worst topographical nature possible, and, although in one of the oldest States of the Union
, there were but few reliable maps.
Consequently, this information had to be obtained in advance of the army.
A party composed of regular and volunteer officers and soldiers, under Colonel N. Michler
, of the Engineer Corps, was directed to undertake this work.
Their labors commenced after crossing the Rapidan
Every road within the lines of the army had to be surveyed and mapped, and the work extended as far as possible to the front and the flanks.
The maps were immediately reproduced on the field and distributed as far as time would permit.
Revised editions of the maps were published as often as new information was collected.
In this way, several editions of eleven maps were arranged and issued, comprising surveys covering an area of seven hundred and thirty square miles.
These were also corrected by instruments carried by the supply train and by maps captured from the Confederates
Before the army started from its winter quarters on the north of the Rapidan
, in the spring of 1864, for the last great campaign, there had been twelve hundred maps made and issued.
After the start, and before the end of the siege of Petersburg
, about sixteen hundred were issued from new surveys.
In addition to the duties of surveying the country and making and distributing maps, the officers of the corps were charged with the work of selecting positions and directing their fortification.
On the morning of the 3d of June, a gallant assault by the whole Union army was directed against