Except for map sheet 31, soil polygons were traced on to mylar overlays.
These overlays were scanned at 400 dpi in 2 sections per map sheet (east &
west). They were vectorized in Arc/Info, merged into a single file, and converted
from digitizer coordinates into State Plane, California Zone II, NAD27 feet
coordinates using the X, Y tics from the map sheets in the soil survey. They
were then reprojected to UTM, Zone 10, NAD27 coordinates to be consistent
with the rest of our GIS database. Vectors errors such as dangling arcs, unclosed
polygons, or scanning artifacts were removed. Arcs were attributed with their
source (digitizing, scanning, or on-screen digitizing) and polygons were attributed
with their soils series code and a numeric equivalent created by the IHRMP
North Coast GIS Lab. All map sheets were merged together into a single layer
in Arc/Info. This single layer was projected into State Plane, California
Zone II, NAD27 feet projections & Albers Equal Area, NAD27 meters projections
so that a wider audience could use our data. An ArcView shapefile version
of the UTM, NAD27 coverage was also created. For map sheet 31, data were digitized
using a digitizing tablet.
For the Sonoma Valley portion, the set of polygons from the original work
was moved using an XY shift. The distance values of the shift were calculated
as an average discrepancy from several control points to more closely resemble
the intended locations of the soil survey polygons in the context of the
DOQQs. Map sheets for the remaining areas of Sonoma Creek watershed were
scanned from the Soil Survey book and georeferenced in ArcView using 3-5
control points and ImageAnalyst. The polygons were digitized from the scans
using heads-up methods in ArcView. The new polygons were edgematched in
groups using ArcInfo and digitizing/edgematching errors were cleaned in
ArcEdit before coverage topology was rebuilt. This work was done between
March 2001 and February 2002. "