Preliminary quaternary geologic maps of Santa Clara Valley, Santa Clara, Alameda, and San Mateo counties, California: A digital database

The geologic map information was digitized from stable originals of the geologic maps at 1:24,000 scale. The author manuscripts (ink on mylar) were scanned using a Tektronix 4991 monochrome scanner with a resolution of 304.8 dots per inch. The scanned images were vectorized and transformed from scanner coordinates to projection coordinates with digital tics placed by hand at quadrangle corners. The scanned lines were edited interactively by hand using ALACARTE, color boundaries were tagged as a contact or fault as appropriate, and scanning artifacts visible at 1:24,000 were removed. Quadrangle boundaries are included in each coverage to retain the integrity of units in each quadrangle, except in cal_utm where a large area of undifferentiated bedrock was placed outside the map boundary to allow convenient placement of the map explanation.
Base Map layers were prepared from scale-stable printing negatives of the U.S. Geological Survey Palo Alto (1982 edition) and San Jose (1978 edition) 1:100,000 topographic maps. Scanned and vectorized images were transformed from scanner coordinates to projection coordinates with digital tics placed by hand at map corners. The images were then trimmed interactively by hand using ALACARTE to conform to the area of the geologic coverages, and the Palo Alto and San Jose portions were combined.