USGS Digital Raster Graphic 1:250,000 and 1:63,360 Quadrangles

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Frequently anticipated questions:

What does this data set describe?

Title: USGS Digital Raster Graphic 1:250,000 and 1:63,360 Quadrangles
The Digital Raster Graphic (DRG) is a raster image of a scanned USGS topographic map. The collar information has been stripped off and the resulting image georeferenced to the Alaska Albers NAD83 grid
  1. How should this data set be cited?

    USGS, 19970610, USGS Digital Raster Graphic 1:250,000 and 1:63,360 Quadrangles: USGS, Reston, VA.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: 157.55125214
    East_Bounding_Coordinate: 117.38252248
    North_Bounding_Coordinate: 67.56587136
    South_Bounding_Coordinate: 49.12879913

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Calendar_Date: 01-Jan-2007
    Currentness_Reference: "Ground Condition"

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: map

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Raster data set. It contains the following raster data types:

      • Dimensions 6769 x 5445, type Pixel

    2. What coordinate system is used to represent geographic features?

      The map projection used is Albers Conical Equal Area.

      Projection parameters:
      Standard_Parallel: 55.000000
      Standard_Parallel: 65.000000
      Longitude_of_Central_Meridian: -154.000000
      Latitude_of_Projection_Origin: 50.000000
      False_Easting: 0.000000
      False_Northing: 0.000000

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.000100
      Ordinates (y-coordinates) are specified to the nearest 0.000100
      Planar coordinates are specified in meters

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.

  7. How does the data set describe geographic features?

    Each raster entity or pixel contains a color index from 0 through 12 referencing a color palette of RGB values from 0 through 255 in which the standard colors used in the DRG are defined.
    USGS DRG Color Palette
    Digital Number Color Red Green Blue
    0 Black 0 0 0 1 White 255 255 255 2 Blue 0 151 164 3 Red 203 0 23 4 Brown 131 66 37 5 Green 201 234 157 6 Purple 137 51 128 7 Yellow 255 234 0 8 Light Blue 167 226 226 9 Light Red 255 184 184 10 Light Purple 218 179 214 11 Light Grey 209 209 209 12 Light Brown 207 164 142
    Draft Standards for Digital Raster Graphic.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

    This DRG was produced through an Innovative Partnership agreement between The Land Information Technology Company, Ltd., of Aurora, CO and the USGS.

  3. To whom should users address questions about the data?

Why was the data set created?

A DRG is useful as a source or background layer in a GIS, as a means to perform quality assurance on other digital products, and as a source for the collection and revision of DLG data. DRG's can also be merged with other digital data, e.g. DEM's or DOQ's, to produce a hybrid digital file.

How was the data set created?

  1. From what previous works were the data drawn?

    map1 (source 1 of 1)
    USGS, 1985, Portair SW: USGS, Reston, VA.

    Type_of_Source_Media: "paper"
    Source_Scale_Denominator: 24000
    Source_Contribution: The source map is scanned to produce the DRG.

  2. How were the data generated, processed, and modified?

    Date: 10-Jun-1997 (process 1 of 1)
    The production procedures, instrumentation, hardware, and software used in the collection of standard DRG products vary depending on systems used at the contract, cooperator or USGS production sites. The majority of DRG data sets are acquired through government contract. The process step describes, in general, the process used in the production of standard DRG data sets.
    1. Production of a DRG begins with the scanning of a paper 7.5-minute topographic map (map1) on a high-resolution scanner. Scanning resolutions range from 500 - 1000 dpi with the output file running between 160-300 mb.
    2. Removal of screens (descreening) and color quantization to reduce the number of colors also takes place during the scanning phase.
    3. The raw scan file is then transformed and georeferenced using UTM coordinates of the sixteen 2.5-minute grid ticks, which are obtained using the in-house produced program COORDAT and stored in a ground control file. Those sixteen 2.5-minute ticks are interactively visited and assigned their respective UTM coordinates. USGS program XSHAPES4 then performs a piecewise linear rubber sheet transformation.
    to resample the file to 250 dpi.
    5. The image file is converted to a TIFF and further reduced by converting the file to a run length encoding Packbits compression(type 32773).
    6. The color palette of the compressed DRG is then standardized by replacing the original RGB values assigned during the scanning process with standard RGB value combinations using the in-house produced TIFFREMAP program.
    7. Prior to archiving the DRG undergoes the following quality assurance procedures:
    a. The color index values of each DRG are checked to ensure the RGB combinations are consistent with the standardized color palette.
    b. All DRG files are inspected to ensure that they are geometrically consistent with normal map presentation.
    c. Selected DRG's are checked to ensure that data elements in the DRG metadata file correspond to the map collar information and to the information in the associated image file.
    d. Selected DRG's are checked for georeferencing accuracy by comparing the book value of latitude and longitude tick marks with corresponding tick intersections in the DRG image.
    e. Transformations are checked on selected DRG's by comparing the positions of well defined points, such as UTM grid intersections in the graphic product, with the corresponding image points in the DRG.
    USGS DRG production specifications are available on request from the National Mapping Division and Mid-Continent Mapping Center by contacting:
    Rolla-ESIC U.S. Geological Survey 1400 Independence Rd., MS231 Rolla, MO 65401-2602 Phone (573)308-3500 Facsimile (573)308-3615 E-mail to World Wide Web: <>

    Data sources used in this process:

    • map1

  3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

    The DRG is an 8-bit color image that employs a color palette to ensure uniform colors throughout a particular DRG series. All DRG's within a series must have the same RGB value.

  2. How accurate are the geographic locations?

    While the datum of the published map is retained to be consistent with other USGS digital data, this image is cast on the UTM and may be INCONSISTENT with the credit note on the image collar.

  3. How accurate are the heights or depths?

    Refer to the DRG collar for information about vertical positional accuracy.

  4. Where are the gaps in the data? What is missing?

    The DRG is a faithfully reproduced digital image of the original source map. Some differences may be detected between the source graphic used and the DRG due to the RGB values assigned that particular color. The intent is to recreate those colors as near as possible. Data completeness for DRG files reflect content of the source graphic. Features may have been eliminated or generalized on the source graphic due to scale and legibility constraints. For information on collection and inclusion criteria, see U.S. Geological Survey, 1994, Standards for 1:24,000-Scale Digital Line Graphs and Quadrangle Maps: National Mapping Program Technical Instructions and U.S. Geological Survey, 1994, Standards for Digital Line Graphs: National Mapping Program Technical Instructions.

  5. How consistent are the relationships among the observations, including topology?

    Not Applicable

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: "None"
Acknowledgment of the USGS would be appreciated in products derived from these data.

  1. Who distributes the data set? (Distributor 1 of 1)

    Earth Science Information Center, U.S. Geological Survey Contact Address
    507 National Center
    Reston, Virginia 22092

    1 800 USA MAPS (voice)

  2. What's the catalog number I need to order this data set?

  3. What legal disclaimers am I supposed to read?

    Although these data have been processed successfully on a computer system at the USGS, no warranty expressed or implied is made by the USGS regarding the use of the data on any other system, nor does the act of distribution constitute any such warranty. The USGS will warrant the delivery of this product in computer-readable format and will offer appropriate adjustment of credit when the product is determined unreadable by correctly adjusted computer input peripherals, or when the physical medium is delivered in damaged condition. Requests for adjustment of credit must be made within 90 days from the date of this shipment from the ordering site.

  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 10-Jun-1997
Metadata author:
U.S. Geological Survey
590 National Center
Reston, Virginia 22092

1 703 648 4533 (voice)
Copies of this publication are available from anonymous File Transfer Protocol (anonymous FTP); <>

Metadata standard:
"Content Standards for Digital Geospatial Metadata" (FGDC-STD-001-1998)

Generated by mp version 2.9.20 on Thu Apr 28 13:02:28 2016