For decades, USGS topographic quadrangle maps have been used by geologists as the base for geologic mapping applications. USGS topographic maps have provided con¬sistently high-quality map data and symbolization (fig. 1). A variety of derived products has been created from these topo¬graphic quadrangle maps, including greenline sheets, scans of the paper maps, Digital Raster Graphics (DRG), Digital Line Graphs (DLG), and Raster Feature Separates (RFS). When the USGS ceased to update and revise the pa¬per topographic maps, the currency of many geographic areas has gradually become unacceptable. For example, “Provi¬sional Edition” USGS maps created with metric contours have not been updated to be consistent with the standard contours in feet. DLG feature layers were never completed for many states, first generation DRGs are too coarse in resolution, second generation DRGs were never completed nationwide, and RFS products are no longer produced by the USGS. Many states have been left with incomplete digital base data and quadrangle maps that are significantly out of date.
|Name||Open-File Report - U.S.Geological Survey|