That depends on what kind of reprojection you want to do. In some cases, if you want to reproject from one datum to another (specifically NAD 27 to NAD 83, or NAD 83 to NAD 27), a simple x-y shift will suffice.
Yes, customers will need to acquire at least 2 consecutive digital images from the same roll and then create transparencies or contact prints to view them with a stereoscope.
A feature is something shown on a map, and it has characteristics or properties, which can be represented in feature-based Digital Line Graph (DLG) data using attributes and values.
Yes.  Scanning of the EROS film archives is following a plan to capture images from rolls at risk of decay from vinegar syndrome. Science requirements are also reviewed on a regular basis, but a formal, on-line schedule is not available at this time.
Almost 180,000 USGS historical topographic maps are available free of charge as PDF documents. This set of files is referred to as the Historical Topographic Map Collection (HTMC). 
For links and procedures for free download of PDF topographic maps, both current US Topo maps and the Historical Topographic Map Collection
Geographically, and as a general reference, the United States (short form of the official name, United States of America) includes all areas considered under the sovereignty of the United States, but does not include leased areas.
From the completion of the original 7.5-minute map series in 1992 until late 2008, the USGS mapping program focused on creating national geographic information system (GIS) databases. In Nov