According to the USGS Website "The U.S. Geological Survey's (USGS) digital line graph (DLG) files are digital vector representations of cartographic information. Data files of topographic and planimetric map features are derived from either aerial photographs or from cartographic source materials using manual and automated digitizing methods." The following map is from downtown Savannah, GA.




http://ga.water.usgs.gov/olympics/sav.sm.dlg.html