STATUS OF THE NATION’S GEOLOGIC MAP COVERAGE

Systematic geologic mapping of the United States has been conducted for more than 125 years. In the period centered on 1895-1920, the USGS conducted its first such program, the Geologic Atlas of the United States. In more recent times, geologic mapping has been conducted under many programs in Federal, State, and other agencies. These programs have differed in emphasis owing to funding source and time period; partly as the result, geologic maps vary significantly in content and format. These differences present a real challenge to the preparation of index maps that purport to show geologic map coverage - if all geologic maps are not alike in content, scale, detail, vintage, or currency, which then should be included in an index map? By what criteria should we differentiate or classify geologic maps for this purpose?

The principal and most obvious purpose for index maps is to convey to any user, whether a practicing geologist or a homeowner, the availability of published geologic maps, and to aid the Nation’s geological surveys as they prioritize areas that should be mapped in the future (or remapped, usually in more detail). But increasingly, it’s become of paramount importance to demonstrate to legislators and oversight agencies such as the U.S. Office of Management and Budget (OMB) that funding has produced tangible results.

In response to requests from the Association of American State Geologists (AASG) and the USGS National Cooperative Geologic Mapping Program (NCGMP), the National Geologic Map Database project (NGMDB) in 2005 developed the capability to generate index maps showing geologic map coverage at different scales and for various time periods (see example at https://ngmdb.usgs.gov/Info/reports/). The information supplied by the NGMDB (i.e., index maps and numeric summaries of the extent of intermediate and large-scale geologic mapping in the U.S.) fulfills OMB requirements for NCGMP “performance metrics”. These metrics serve as partial documentation of AASG and USGS performance in addressing the goals of the Geologic Mapping Act. In response to the increasing demand for such information, the NGMDB is revisiting this method, to improve the accuracy of content and response time.