manifold.net has converted the entire, 14 CD series of 1:100,000-scale USGS digital maps into Manifold format.

Many of the original USGS CDs were not completely full, so by better arranging the files, we have been able to republish the set in seven CDs, each of which covers a logical geographic region and which provide some overlap with neighboring CD sets (illustration above). 

Plotting the 22,000 significant US population centers on a map of USGS "quad" maps allowed us to allocate maps to CDs in a way that minimizes CD boundary crossings over major population centers, so it is more likely that you will not have to change CDs frequently.  Note how an overview plot of population centers (above) reveals how settlement followed Appalachian mountain topography in the Southeast, proceeded West along river valleys in the Plains states, and extended along the great North / South valleys of California and the Northwest states.

Visit the manifold.net 100kDLG FTP site to download any of the above maps.