Grant's overland campaign primarily was over ground that both armies had been marching over for more than three years. If you take a narrow 40 mile stretch from Fredericksburg to Richmond there maybe some unfamiliar ground but Union cavalry and spies had been all over that area. East of Richmond was the area in which the Peninsular Campaign was fought; The Wilderness was a cannon shot away from the battlefields of Chancelorsville. Below is proof that the Grant's Army had an outstanding Engineering Corps providing an enormous amount of topo data.
From the O.R. Series I, Vol. 36, page 293. Report of Maj. Nathaniel Michler, Corps of Engineers, U.S. Army, Acting Chief Engineer. HDQRS. Army of the Potomac, Engineer Department, Oct. 20. 1864.
Department of Southeast Virginia and Fort Monroe, compiled in the Bureau of Topographical Engineers of the War Department, scale 1/200000 inch. The Bureau also kindly furnished others for reference, viz: Part of the map of the Military Department of Southeast Virginia and Fort Monroe, showing the approaches to Richmond and Petersburg, scale 1/8000 inch, and Nos. 1, 2, and 3 of the Peninsular Campaign maps, together with the Henrico County map, the former engraved, and the two latter photographed for the use of the armies operating against Richmond. The detailed map of Northeast Virginia and vicinity of Washington, scale 1 inch to the mile, compiled under the direction of Maj. A. W. Whipple, U. S. Topographical Engineers, was also placed at the disposal of this department. At different intervals during the several months previous to the opening of the spring campaign a great many reconnaissances and surveys had been pushed as far as the different fords of the Rapidan and that section ot the country had become accurately known. The movements of the army in November and December, 1863, between the Rapidan and Mine Run, had also furnished some very important information which subsequently proved of great value. Beyond the latter narrow strip of local knowledge along the Rapidan, the experience gained in the memorable campaign of the Army of the Potomac during the months of May and June of 1864 showed very conclusively that however well the only accessible maps might have served the purposes of general knowledge, still they furnish but little of that detailed information so necessary in selecting and ordering the different routes of marching columns, and were too decidedly deficient in accuracy and detail to enable a general to maneuver with certainty his troops in the face of a brave and ever- watchful enemy. This was more especially the case as the country in itself proved to be of the worst and most impracticable character a most difficult one for executing any combined movement. This may appear strange to those who reflect that the Commonwealth of Virginia is among the oldest of the States of the Union. They necessarily conclude that her archives should contain the most perfect geographical and topographical material for mapping her extensive domains. The proof that such has not been the case, and that this great want has been felt by her own military officers, is shown by the large surveying parties kept by them constantly in the field. Some of the results of their labors have lately fallen into my hands, a few excellent maps having been captured which bear evidence of very recent construction. On the face of them not only appear their familiar names, but the distinguishing peculiarities of workmanship of assistants employed on different Government surveys at the very commencement of the war. Although the enemy has no doubt suffered at times from want of accurate maps, still he at all times possessed a superior knowledge of the country, and could always obtain reliable guides from among its inhabitants, thus affording him a very great advantage over his adversary. In order to be able to cope with him with anything like equal advantage it soon became apparent that the difficulties to which reference has been made would not only have to be overcome by gathering mate. rial with the onward march of the army, but that the desired information would have to be obtained in anticipation of any move. To accomplish this the officers and assistants of my party were kept constantly occupied both day and night; they were not only called upon to prepare the much needed maps with the detailed corrections, but also in the entire absence of reliable guides to act as such to the different columns, either as they moved along their respective routes of march or while maneuvering for favorable positions previous to an attack. Maj. John E. Weiss, commissioned by the Governor of the State of Kentucky, acted as my principal assistant, and Capt. W. II. Paine, additional aide-de-camp, was also attached to the Engineer Depart- ment as an assistant. In addition to these there were seven civil assistants, besides several men detailed from the ranks to act in various capacities. The names of the former are Mr. Ferd. Theilkuhl, W. Burchard, Franz Schumann, E. Myers, L. C. Oswell, George L. Crane, and John H. Mullen. Some of them had been connected for a long time with the Army of the Potomac, and had gained great ex- perience in making rapid reconnaissances and surveys, and in execut- ing topographical sketches. Their duties commenced immediately after crossing the Rapidan, the surveys being connected with those previously extended to that river, and progressed without interrup- tion or re~t until the army arrived in front of Petersburg; nor- did they then cease, but have continued along without any interruption to the present time. Each and every road within the lines of the army was examined and surveyed, and their researches were pushed as far to the front and on the flanks as it was compatible with safety to go without incurring any unnecessary risk of capture. The notes were immediately plotted and the maps compiled and at once photographed for the use of the officers of the command. In addi- tion to the general topographical features of the country being represented, the respective lines of battle taken up at different times and at various localities were located. These were executed under the fire of the sharpshooters, and as well as the constant daily fighting would permit. As rapidly as any new information could be procured new editions of the maps would be prepared and photographed, and widely distributed. In this way, from the crossing of the Rapidan on the 4th of May to the explosion of the mine on the 30th of July, severah editions of each of eleven separate sheets were arranged and issued, comprising surveys which cover an area of 737 square miles. In addition to the surveys already referred to there were several others not embraced on the photograph sketches, com- prism g one from the Germanna Ford to Petersburg, taken by the headquarters train of wagons along which the measurements were made by an odometer, a distance of over 179 miles, and also those niade in company with the cavalry expeditions under Major-General Sheridan, the first from Chancellorsville to Haxalls Lauding on the James River, and the last from Cold Harbor to Trevilian Station on the Virginia Central road and back to the White House, in the ag- gregate a distance of 310 miles. These actual surveys have since been compiled with information obtained from maps captured from the enemy, and the original series of campaign sheets corrected by this additional matter. Six sheets have thus been improved upon, including those styled Culpeper, Chancellorsville, Fredericksburg, Hanover, Richmond, and Petersburg, the originals of the first five of which are in the hands of the engraver, having been previously photographed for any immediate use. On the 9th of July, the date of the order directing that the oper- ations of this army against the intrenched position of the enemy de- fending Petersburg will be by regular approaches, a trigonometrical survey of the environs of that city was commenced, showing the topographical features of the country and the positions of the in- trenched lines of both armies, and by the 30th of the same month was far advanced. During the progress of the siege this map proved of the greatest importance, and constant reference was made to it. In closing this part of the report in relation to the labors of the topographical department of the army dnring the period called for by the major-general commanding, it may be of interest to know that over 1,300 miles of actual surveys were made; that more than 1,200 maps were issued to the army previous to taking up the line of march across the iRapidan, and over 1,600 photograph sketches between that date aud the 30th of July. It would not be just to my assistants to refrain from expressing the appreciation I entertain for the unwavering and cheerful energy at all times displayed by them in the performance of their duties. The amount and accuracy of the work accomplished by them is sufficient evidence of their activity and ability. Exposed night and day to all the hardships and dangers of the campaign, it was under the most trying circumstances that their duties were performed. The usual conveniences afforded persons so employed were necessarily denied to them, but they were ever ready for any emergency and prompt to execnte any instructions. The particular attention of the command- ing general is called to the extent and difficulty of the labors per- formed by them. The silent and arduous labors of the engineer, upon which depends to such a great extent the success of a campaign, are too apt to be forgotten and overshadowed by the brilliancy of the noble and brave deeds of other arms of the service. In this report it will be unnecessary to enter into great detail upon the many various engineering operations of the campaign aside from the one branch of duty already alluded to, particularly as some of them have been elaborately presented in accompanying documents, nor will an accurate description of the country passed over be attempted, as it will no doubt be more vividly pictured by others. The portfolio of maps* which is appeuded to this paper must for the present exhibit the lines of operations of the army and the localities of the various fields of battle until additional time and more advantageous circumstances permit the perfecting of them. Exact and beautiful drawings of the several points of interest are in course of construction...