THE OREGON GEOLOGIC DATA COMPILATION: SOUTHEAST OREGON

The Oregon Department of Geology and Mineral Industries is developing a new digital geologic compilation map for Oregon which 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 mapping is low resolution (1:500,000) and generalized. 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 making a new compilation map for the state we could chose to draw entirely new geology polygons by interpreting and synthesizing existing mapping, but 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. Instead, we decided to take advantage of the power of GIS and database technology to develop a new type of compilation. We converted all of the existing mapping for the area into vector form by tracing the original paper maps, scanning the traced images and georeferencing, vectorizing and annotating those scans. 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 which presents the best available data at any point, and preserves all of the original detail of the source map. In order to organize and unify the thousands of geologic units resulting from this process, we use a group of geology subject matter experts to assign geologic merge units to each unit on the map, this allows display of a “logically seamless” compilation map that links units across source map boundaries while leaving the original source data intact. We also made an interpretation of the engineering lithologic properties for each unit, to aid engineers and soil scientists in using the data. The second portion of this map was completed in 2005, and covers the southeast portion of the state. Building on our experience with the northeast Oregon compilation, we have made several changes in database structure, and revamped our lithologic merge information for engineering use. The new geologic format allows for more refined searches for stratigraphic and lithologic units from the interpreted data.