A NEW DIGITAL GEOLOGIC MAP FOR OREGON

The Oregon Department of Geology and Mineral Industries is developing a new digital geologic compilation map for Oregon, funded in part by the USGS STATEMAP program. The map recognizes a 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. Existing statewide geologic mapping is low resolution (1:500,000) and gives very generalized geologic information. Published geologic mapping for any part of the state ranges greatly in resolution and quality, with much of the state only mapped at reconnaissance scales. In preparing a new compilation map for the state, we were faced with a difficult choice in preparing a traditional compilation map. If we chose to draw entirely new geology polygons by interpreting and synthesizing existing mapping, we would either have to invent substantial amounts of new geology in area mapped at low resolution, or ignore substantial amounts of detail in areas of higher resolution. In either case, critical information contained in the original mapping would be obscured. Instead, we decided to take advantage of the power of GIS and database technology to develop a new type of compilation. We first converted all of the existing mapping for our NE Oregon Pilot area into vector GIS form by tracing the original paper maps, scanning the traced images and georeferencing, vectorizing and annotating those images. Concurrently we entered all of the data from the unit descriptions in each map into an Access database. We then chose, for any given area, the best mapping available, and appended all of the best polygons into a complete coverage of the area. This map then presents the best available data at any point, and preserves all of the original detail of the source map. This product however is full of boundary faults, as no units match across map borders. We then grouped all of the geology units in the map area into regional stratigraphic units and lithologic units. This provides a means to link polygons of like stratigraphic unit across the original map borders to provide a more seamless map. This new map, and the linked database, should provide users with the best available information in any area of interest, with all of the original detail, while at the same time providing more regional perspectives.