UTM coordinates are measured on the map by subdividing the 1000 meter grid squares into tenths or hundredths. This will narrow down the coordinate to a 100 or 10 meter square.
Generally, for the conterminous United States, the North American Datum (NAD) shift amounts to about 210 meters. This shift occurs because of the change in shape of the spheroid used to define the datum.
An exhaustive database that provides bibliographic access to thousands of geologic, geophysical, and other kinds of maps available in USGS publications, Web sites, and in popular science journals.
EROS has digitized over 6.4 million frames of aerial film creating medium-resolution digital images (400dpi) and associated browse images for on-line viewing.
No. A photographic enlargement only appears to show more detail than a 9-by-9 inch photograph. Photographic resolution (or image resolution) deteriorates with each enlargement factor.
YES, Visit our National Geospatial Program page or call 1-888-ASK-USGS for our information package on digital cartographic data. 
Almost 179,000 USGS historical topographic maps are available free of charge as PDF documents.
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.
It will probably take approximately 5 years to digitize the archive. A priority scheme is being developed and will be made available to the public at a later date.
The public may download digital aerial photography products at no cost from the Earth Resources Observation and Scienc