High-resolution digital copy of the map made as a courtesy by the National Archives and delivered to the Maryland State Archives May 15, 2006 by Rick Blondo.
Here is all the information I have pertaining to the Howard County Confederate map.
The back of the map has this information typed onto a NARA form:
Records of the Office of the Chief of Engineers
Record Group 77
Subgroup b
Series: Headquarters Map File
Filed as US 253-4
The Cartographic Research Room in the National Archives at College Park has an index comprised of a series of grey-boxed cards organized by state (Maryland has one box) containing an index to maps, drawings, etc. filed chronologically. There are many interesting items indexed in this box. Two examples are an 1860s map showing Confederate troop positions around Williamsport, Maryland and a 1935 map of Baltimore City showing the configuration of the underlying rock floor based on information secured by C.W.A. workers done by the Bureau of Plans and Surveys showing topography, streets, railroads, roads, individual structures, and ship channels (35” x 28”). There are several record groups represented in this index. The index card for the Howard County Confederate map includes the below information. Note: There are several entries listed on the card. Entry 4 is the map in question. Entry 4a indicates there is a partially completed copy of Entry 4.
RG 77 Chief of Engineers
Civil Works Map File
Maryland
U.S. 253 Roll
Confederate Maps 1861 – 1865
4. Map of Howard County, Maryland
Engineer Office, First Corps, A.N.V. Scale, ________
(small); p. ms.
image - howard_co_1861.tif