Scanning and Georeferencing Historical USGS Quadrangles
http://pubs.usgs.gov/fs/2011/3009/

What is this project about?
As part of the new National Map the United States Geological Survey
intends to provide digital images of all its historical topographic
quadrangles. Users will have access to 180,000 7.5 minute (1:24000)
quadrangles and another 120,000 maps at other scales. Contractors are
creating these images by scanning paper maps at resolutions of 500-600
dots per inch. Thus the scans are essentially perfect facsimiles of
the existing printed archive.
Full utility of the scanned images requires that they be
"georeferenced", that is, the images must be tied to a known
coordinate system. For example, without georeferencing there would be
no way to overlay the maps on other layers comprising the National
Map, nor would it be possible to assemble a seamless image from
adjoining scans.
Existing georeferencing software employs what is essentially a manual
procedure requiring users to digitize known locations on the screen
and enter text in dialog boxes. At about 20 minutes per scan, more
than 45 person-years would be needed to georeference the entire set of
scanned images. This far exceeds available resources.
Our project aims to replace the manual process with an automated
procedure that can process large numbers of scans with no operator
supervision.

QUAD-G – Automated Georeferencing Project
http://www.geography.wisc.edu/research/projects/QUAD-G/
http://pubs.usgs.gov/fs/2011/3009/

-- 
Smoke Pfeiffer

Laws do not represent either reason or justice.
They represent force.