the USGS DDS contains geochemical data, collected under the NURE program, that covers the western half of the United States. This disc contains nearly 400,000 sample records compiled by the USGS and the Department of Energy over many years. These records are accessed by using a retrieval system called GSSEARCH that provides answers to complicated searches within seconds. Subsets of data can easily be created from the CD-ROM and passed through other processing programs, such as statistical packages for detailed analysis and display. Probably the most significant aspect of the NURE CD-ROM is that now hundreds of scientists and researchers will be able to have their own copy of this massive data base directly accessible through their desktop computers or workstations.

Geology of Nevada. -The second release in the DDS represents an important milestone for the USGS. This disc contains the first geologic map in digital form placed on a CD-ROM. The accompanying display software called MAPPER was also developed by the USGS and provides a soft-copy version of the geologic map of Nevada, displayable on inexpensive personal computers equipped with color monitors (fig. 2). This disc is not intended to replace the printed map but to complement it. The software allows the user to zoom into an area of interest and display the color geologic formations (along with a variety of other information) at resolutions that bring out minute detail. In addition, subtle or obscure geologic formations can easily be highlighted and identified in conjunction with the color key chart (fig. 3).

The US GeoData Series. - US GeoData are CD-ROM's that contain cartographic and textual data in digital form. The US GeoData Series includes (but is not limited to) the standard USGS digital line graph map series (1:24,000, 1:100,000, 1:250,000, etc.). Other data included in the US GeoData Series are Geographic Names Information System data and 1:100,000-scale digital elevation model data.

Many other CD-ROM discs are being developed at the USGS. One very interesting disc will contain high-resolution color images of core samples and related geophysical information, thus allowing the user to preview

these valuable geological archives anywhere in the world. Another disc will provide a combination of sonar, bathymetric, spatial, and attribute information about the bottom of the Boston harbor, including actual color-digitized photographs of selected areas.

Significant economic reasons support the Federal Government's increasing use of CD-ROM. The use of this technology can produce considerable reductions in the cost of accessing and disseminating information. Not only can agencies internally distribute. mainframe-sized data bases on these inexpensive discs, but also the public now has access to these same data bases at significantly reduced cost. For example, the digital mapping data produced by the USGS in the form of the nationwide cartographic data base, at 1:2,000,000 scale, previously cost more than $1,400 when purchased on multiple reels of magnetic tape. It can now (1991) be purchased at any USGS Earth Science Information Center on a single CD-ROM, including display software, for $32. The first in a series of 1:100,000-scale digital mapping discs is just now being released and will offer even more cost savings to the public.

USGS Programs

cientific programs are administered through the Geologic, Water Resources, and National Mapping Divisions and supported by the Information Systems and Administrative Divisions. The National Center of the USGS is located in Reston, Va., near Washington, D.C. Research and investigations are carried out through an extensive organization of regional and field offices located throughout the 50 States, Puerto Rico, the Virgin Islands, and the Territory of Guam.

he headquarters office of the National Mapping Division is located in Reston, Va., and is composed of five primary organizational units: Program, Budget, and Administration; Coordination and Requirements; Production Management; Research; and Information and Data Services. Four mapping centers (Reston, Va.; Rolla, Mo.; Denver, Colo.; and Menlo Park, Calif.) and the EROS (Earth Resources Observation Systems) Data Center (Sioux Falls, S. Dak.) perform operational mapping, remote sensing, printing, product distribution, and data dissemination activities.

Mapping Coordination.-The USGS annually coordinates requirements for maps and digital cartographic data of Federal agencies under authority of Office of Management and Budget (OMB) Circular A-16. In October 1990, OMB revised Circular A-16 to broaden the scope of Federal spatial data activities to be coordinated (see article, p. 15). Under the new circular, the USGS also coordinates requirements of State and local agencies for maps and map-related products. In the area of digital cartography, the USGS chairs both the Interior Geographic Data Committee (a departmental committee) and the Federal Geographic Data Committee (a multiagency committee) established under the new Circular A-16. The USGS provides leadership in the use of spatial data and in the development of digital data exchange standards. The USGS also provides staff support to the U.S. Board on Geographic Names, an interdepartmental board that determines the choice, form, spelling, and application of official geographic place names for Federal use.

Map and Digital Data Production. - The USGS prepares base maps, image map products, digital cartographic and geographic data, and selected thematic maps of the Nation that are used extensively for land planning, land and resource management, and recreation purposes. Of rapidly increasing importance is the production of digital geographic data in various electronic media. Reproductions of aerial photographs and satellite images also

are available. Digital data are available from the National Digital Cartographic Data Base as digital line graphs or digital elevation models.

Primary topographic maps, including 7.5-minute maps mostly at 1:24,000 scale for all areas of the lower 49 States and 15-minute maps of Alaska at 1:63,360 scale, are especially useful where detailed information is needed for all types of land and resource management. These detailed maps are periodically inspected and revised to maintain data currentness.

Also available are smaller scale topographic maps, such as the intermediate-scale maps prepared at 1:100,000 scale and the 1:250,000-scale map series. These map series are widely used by Federal and State agencies and the private sector for preparing their own special-purpose maps and depicting their unique data. Other maps available include 1:500,000-scale State base maps and smaller scale U.S. base maps.

The land use and land cover maps, primarily at scales of 1:250,000 and 1:100,000 for selected areas, provide the only systematic nationwide inventory of land use and land cover data. The USGS also prepares special-purpose map products, such as orthophotoquads, small-scale image maps, U.S. National Park maps, and thematic maps.

Research and Technology.-The USGS has pioneered investigations that have led to significant developments and changes in surveying and mapping. Mapping research activities, which are centered primarily on the geographic and cartographic disciplines, currently emphasize spatial data analysis, applications of remote sensing and geographic information systems, and advanced techniques for producing digital cartographic data.

The Division has embarked on a major research and development plan to move from manual to digital production and revision of map products. The goals of the map modernization effort are to implement the advanced cartographic systems and procedures required to automate map production and to provide digital cartographic data required by Federal and State agencies for computer-based analysis of spatial data.

Information Services.-The USGS disseminates much of the Nation's earth science information through its Earth Science Information Centers (ESIC), 62 State ESICaffiliated offices, and the Tennessee Valley Authority. The information is provided in many forms, from maps and books to computer-readable magnetic tapes and compact discs. About 130,000 different maps, books, and reports and about 9.5 million aerial and space images are available for purchase. USGS maps are also available