Vegetation types were defined by descriptors used in the survey notes, supplemented when needed by distances to witness trees as recorded in the notes. Coverage was delineated using distances recorded as points along the survey lines. Vegetation in the interiors of sections was delineated using features depicted on the surveyor's township plat maps, historic air photos, modern soil maps, and best professional judgement based on topographic features.
Mylars were digitized by hand early in the project, and later scanned directly into ArcInfo using the ArcScan module. Once in ArcInfo the polygon coverage was built or cleaned with a fuzzy tolerance of 1 meter and polygons were attributed with the veg abbreviation. Edgematching and elimination of sliver polygons was done by hand to avoid losing tiny polygons that were necessary to the coverage (gravel bars, etc.).
Department of Corrections, Division of State Lands, and Oregon State University (Department of Fisheries and Wildlife) have all assisted with digitizing of these topo quads.
The final editing was performed at TNC by John Christy and John Hak. Zipped versions of the shapefiles were transferred to OSU, where Doug Oetter converted them to ARC/INFO vector coverages, and performed subsequent edits.
Version 1 appeared in the Willamette Valley Atlas version 1.
Version 1.1 was completed in January, 1999.
Version 2, which added significant areas to the coverage and separated wet from dry prairie, was completed December, 1999.
Version 3 (January 2000) featured updates to water features and wetlands.
Version 4 (April 2000) edited out unlabled polygons from v.3.
Version 5 (September 2000) added new data from the Sauvie Island area.
Version 6 (June 2002) differs in having (1) all polygons converted from the "stream" layer to the polygon layer, so the stream layer is now just line data, and (2) miscellaneous corrections to veg polygons that won't be obvious.
This coverage has topology, as evidenced by build process, and was cross-checked by GIS technicians at OSU, FSL, and State Corrections. Plots were checked and edited by John Christy, The Nature Conservancy, and Ed Alverson, Oregon Natural Heritage Program.
A section line coverage, prepared by Atterbury & Assoc., was used as the grid for placement of survey notations along section lines. It is available from the Oregon State Service Center for GIS. For proper interpretation of vegetation communities identified in this coverage, refer to the associated Word document, veg1851_v5.doc.