OGDC-5: STATEWIDE COVERAGE OF THE OREGON GEOLOGIC DATA COMPILATION

The Oregon Department of Geology and Mineral Industries (DOGAMI) has completed a new digital geologic compilation data set for the state of Oregon, which recognizes the need for a wide range of users to have the best possible geologic data in digital format for hazard assessment, land use management and resource evaluations. The Oregon Geologic Data Compilation (OGDC) provides geologic coverage of the entire state for use in GIS (Geographic Information Systems), along with a relational database of geologic information.

For OGDC, existing geologic maps were scanned, georeferenced, and digitized to preserve the original source map’s detail. The preservation of the original map allows for better resolution and greater detail from maps of a larger scale (up to 1:6000). Previous statewide geologic mapping is at low resolution (1:500,000) and is generalized. Unit descriptions from each map were entered into a relational database which provides a means of joining the original geologic information to the digital unit polygons.

The methodology employed to create OGDC has resulted in an unconventional process of compiling previous geologic mapping. Rather than infer or lose detail by redrawing contacts, map polygons determined to be best available were appended together. In areas of adjacent mapping of varying scale or interpretation, boundary faults occasionally occur but were not fixed or edited. To alleviate this issue, a separate geologic merge unit designation was assigned to each map unit polygon to create a new layer of interpreted geologic information. These merge units allow the appended polygon layer to be displayed with a “logical seamlessness” throughout the state.

The availability of OGDC also provides a valuable resource of data for a number of new maps recently developed by DOGAMI. These maps were created with greatly differing purpose, but all have incorporated OGDC as an essential base element by using the data in its original form, by querying a subset of the data, and by re-interpreting the data. The resulting products are in the form of an interactive web map, a map of statewide landslides, and a map of Oregon’s geologic history, respectively.