The National Oceanic and Atmospheric Administration (NOAA), a subset of the Dept. of Commerce, has archived something like 21,000 historic charts and maps dating from 1747 - 2001. Catalogued as the Office of Coast Survey’s Historical Map and Chart Collection, these items appear to be offered to the public at no charge.

Check it out at: http://chartmaker.ncd.noaa.gov/csdl/ctp/abstract.htm, and then click on “Image Catalog.” When you get to that page, you’ll see several search criteria. Use the “Select a Type” pulldown menu to select "Civil War," which brings up a list of 394 Civil War-related items, which you can then view and download.

For example, I typed “Island No. 10” into the key word field and up popped an 1862 Federal map of the Rebel artillery positions there. Pretty cool resource, I’m thinking.

Sorry if this repeats info from some previous posting.