The generalized landslide zones of Nilsen and Wright (1979, category
5 of plates 1-3) were captured in digital form by scanning publication
negatives. Vector perimeters of the resulting category 5 areas in
the raster scans were determined automatically (GRIDPOLY) and processed
to smooth the boundaries and eliminate polygons with areas less
than 4000-5000 square meters (noise in the data). Registration proved
to be a problem. Initial registration using geographic locations
of various marks on the negatives (determined by
comparison with a base map) was improved by rubbersheeting to better
fit quadrangle corners evident in the data. Most misfits in the
result are probably less than 50 meters on the ground. "
In southeastern Sonoma County, Huffman and Armstrong (1980) provide more tractable information. Envelopes were drawn around these landslides and groups of landslides. Other, local additions were made from Huffman and Armstrong in southern Sonoma County (outside the update areas shown on Figure 1). In the northeastern part of the Bay region, the 1:24,000 landslide maps of Dwyer and others (1976) were similarly used to draw envelopes around landslides and groups of landslides, although numerous small landslides and questionably identified larger landslides were excluded on a case-by-case basis."
Note that no LSCAT values of 4 remain. 4 represented bedrock areas in the input geologic materials polygon layer that were later overlaid by LSCAT categories 5-8.
LSCAT PTYPE
1 unmapped
2 water
3 surficial deposits
5 no mapped landslides (combined with 'few landslides'
on the maps)
6 few landslides
7 many landslides
8 mostly landslide"