Spatial digital database for the geologic map of Oregon

George W. Walker and Norman S. MacLeod compiled the geology on 1:400,000-scale quadrants of the 1982 version of the Oregon topographic basemap.
USGS (National Mapping Division, Thematic Map Unit) personnel digitized and reprojected the compiled geology to the 1982 1:500,000-scale state base map: this work was done on a SCITEX system. The SCITEX files were then converted to an ArcInfo format.

Proof plots were made from the digital files and reviewed by various geologists familar with Oregon geology. A few misidentified polygons were found and the labels corrected. A data model was added and additional attributes coded.
During the initial digitization process, lines representing faults had been captured in a file separate from the geology unit polygons. A USGS contractor edited the fault linework to connect dotted and dashed fault segments into continous lines. Fault type as well as downdrop direction were added as attributes.

For this second edition of the spatial database, the geologic unit and fault coverages were merged to produce a single topology.
Faults forming geologic unit boundaries (contacts) occurred twice in the Raines and others (1996) dataset, once in the fault coverage (coded as a fault) and a second time in the geology coverage (coded as a "contact").
During the process of topologically combining the two coverages, if a fault and a contact were coincident (+/- approx. 300 meters), the contact was eliminated and the remaining line retained the attribute coding inherited from the fault coverage.
The topological combination of geology and fault cover was accomplished as follows:
1) A buffer of fault lines was built with a buffer distance of 300 meters.
2) The buffer was intersected with the geology coverage, thus creating nodes at the approximate ends of sections of arc in the geology coverage that are duplicated by faults.
3) The faults were buffered again, this time at 325 meters. This buffer coverage was used to select the duplicate sections of arcs created in step 2. The selected arcs were deleted.
4) The fault arcs were imported into the geology coverage. Dangling contacts in the coverage were extended to intersect the imported faults. Extensive proofing and editing was required to insure that the geologic unit polygons closed properly against the introduced fault arcs.
The entire ORGEO coverage was rubbersheeted to improve the fit with a georeferenced image of the basemap. The error in registration of the Raines and others (1996) dataset was typically 200-500 meters in the western part, but reached a maximum of 800-900 meters in the eastern third of the map sheet. After adjustment, the registration of the dataset generally is within 200-400 meters. The adjustment was accomplished by defining approximately 200 adjustment links throughout the map area, then interpolating between those links to form a uniform distribution of approximately 10,000 links across the map. The high density of links provided a smooth transition in both direction and magnitude of adjustment from one area of the map to another.
In order allow the dataset to be combined with map databases for adjacent states, modifications were made to database linework near the perimeter of the map area:
1) the map was cropped on the north along the Washington state boundary (generally following the center of the Columbia River).
2) the eastern and southern boundaries were replaced by state boundaries derived from USGS 1:100,000-scale Digital Line Graph (DLG) files.
Staff at the Oregon Department of Geology and Mineral Industries reviewed the resultant geologic map database and identified thirty-one incorrectly labeled polygons. R.J. Miller then incorporated the revisions into the GIS.

Pamela D. Derkey ran mp 2.8.18 on the metadata file, made necessary corrections to the metadata, and imported the metadata into the ORGEO coverage.