The U.S. Geological Survey (USGS), established in 1879, has Federal responsibility for preparing and making multi-purpose maps and fundamental cartographic data to meet the requirements of users throughout the United States. USGS topographic maps are distributed as both paper maps and as scanned raster files referred to as digital raster graphics (DRG) files.
The largest pecentage of DRG data on compact disk recordable (CD-R) media are being produced by the USGS through an Innovative Partnership agreement with The Land Information Technology Company, Ltd., of Aurora, Colorado. This series includes DRGs of USGS standard series quadrangle maps of the United States, its Trusts, and its Territories. The DRG's over most of the State of California are being produced, in cooperation with the USGS, by Teale Data Center in California. Finally, DRG's for parts of Arkansas, Tennessee, North Carolina, South Carolina, Alabama, and Mississippi are being produced by the Tennessee Valley Authority.
The DRGs are georeferenced to the Universal Transverse Mercator (UTM) grid. A DRG may be used as a source or background layer in a geographic information system, as a means to perform quality assurance on other digital products, and as a source for the collection and revision of digital line graph (DLG) data. The DRGs also can be merged with other digital data (e.g., digital elevation model (DEM) or digital orthophotoquad (DOQ) data) to produce a hybrid digital file. These DRG data are produced by the USGS through cooperative agreements with private industry and other Federal, State, and local agencies.
The standard area of coverage of a DRG is the entire area printed on a USGS standard series topographic map including the map collar, any overedge areas, and insets. A status graphic map may be viewed at the following location: USGS Digital Raster Graphics Status Page.
The USGS is producing DRGs from 1:24,000-, 1:24,000/1:25,000-, 1:63,360- (Alaska), 1:100,000-, and 1:250,000-scale topographic map series.
Four items are needed to produce a DRG of a 7.5-minute topographic map:
At the USGS, the first step in the process is to scan a paper 7.5-minute topographic map at 250 dots per inch. The position of each of the sixteen 2.5-minute grid ticks on the image is collected. These ticks are interactively visited and assigned their respective UTM coordinates to rectify and georeference the image to the UTM ground coordinates. A bilinear transformation completes the georeferencing process.
An output resolution of 2.4 meters (8.2 feet) is chosen to resample the file to 250 dots per inch. The image file is converted to a Tagged Image File Format 6.0 image and further reduced by converting the file to a run-length-encoded, PackBit-compressed (type 32773) file.
The color palette of the compressed DRG is then standardized by replacing the original red-green-blue (RGB) values assigned during the scanning process with standard RGB value combinations using the EDC produced TIFFREMAP program.
A DRG is a scanned image of a USGS topographic map. The scanned image includes all map collar information. The image inside the map neatline is georeferenced to the surface of the Earth. The DRG can be used to collect, review, and revise other digital data, such as DLG data. When the DRG is combined with other digital products, such as DOQ or DEM, the resulting image provides additional visual information for the extraction and revision of base cartographic information. The USGS is producing DRGs from 1:24,000-, 1:24,000/1:25,000-, 1:63,360- (Alaska), 1:100,000-, and 1:250,000-scale topographic map series
The DRG uses a standard palette to ensure uniform color throughout a particular map series. The values for a particular color, therefore, will remain consistent throughout that DRG series. Although the color values of the DRG may sometimes match those of the paper source map, a user will usually notice small differences between the colors on the digital image and on the paper map. Also, the quality of the user's monitor affects the DRG color displayed. Although the DRG generally contains the complete content of the source map, features may occasionally be blurred because of substandard source materials. The DRG also may contain misclassified pixels (color noise).
The horizontal positional accuracy of the DRG matches the accuracy of the published source map. To be consistent with other USGS digital data, the image is cast on the UTM projection, and therefore, will not always be consistent with the credit note on the image collar. Only the area inside the map neatline is georeferenced, so minor distortion of the text may occur in the map collar.
The USGS distributes DRGs on CD-R media. Each CD-R includes a scanned image segment of one of the USGS topographic maps for the contiguous States plus Hawaii with either a 1:24,000-scale file, a 1:100,000-scale file, or a 1:250,000-scale file. For Alaska the scale will be either a 1:63,360-scale file or a 1:250,000-scale file.
Coverage of the United States is expected to be completed by the end of 1998.
To place orders and to obtain additional information regarding technical details and pricing schedules, contact: Customer Services, EROS Data Center Earth Science Information Centers (ESICs)
Online requests for these data can be placed via the USGS Global Land Information System (GLIS) worldwide web-based query tool. The GLIS contains metadata and online samples of Earth science data. With GLIS, you may review metadata, determine product availability, and place online requests for products.
The DRGs are available on CD-R by individual files; each individual CD-R includes three files for a pre-selected map scale, which are:
In addition, each CD-R has a readme file found at the head of the CD-R.
No viewing software is made available on the CD-R product; however, this type of software is easily accessible from the USGS Software for Viewing USGS Digital Cartographic Data web site.
A non-technical explanation of possible data corruption problems in USGS DRG products may be viewed at: Problems with GEOTIFF on USGS DRG CD-ROMS.
Applications and Related Data Sets
The DRG is useful as a backdrop onto which other digital data can be overlaid. At the USGS, the DRG is used for validating DLGs and for DLG data collection and revision. Also, the DRG can be used as a tool to assess the completeness of digital data from other mapping agencies. In addition, the DRG can be used to produce "hybrid" products. These products include combined DRGs and DOQs for revising and collecting digital data, DRGs and DEMs for creating shaded-relief DRGs, and combinations of DRG, DOQ, and DLG data. Although a standard DRG is an effective mapping tool, its full potential for digital production is realized in combination with other digital data.
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