Geology of Point Reyes National Seashore and Vicinity, California: A Digital Database

The geologic map information was digitized from stable originals of the geologic maps at 1:48,000 scale. A pencil on mylar overlay of the author manuscript were scanned using a Altek monochrome scanner with a resolution of 800 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 appropriate, and scanning artifacts visible at 1:48,000 were removed. Base map layers were prepared from scale-stable printing negatives of the U.S. Geological Survey Point Reyes National Seashore and Vicinity, California 1:48,000 topographic map, which has an 80-foot contour interval and the U.S. Geological Survey Napa, California 1:100,000 drainage map. 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.