Identification_Information:

  Citation:
    Citation_Information:
      Originator: U.S. Environmental Protection Agency/Office of Water/OST Basins
      Publication_Date: 20070611
      Title:
        USGS 300 Meter Resolution, 1-Degree Digital Elevation Models (DEM) for CONUS,
        Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands
      Publication_Information:
        Publication_Place: Washington DC
        Publisher: US EPA/Office of Water
      Online_Linkage:
        For BASINS model and hydrographic data http://www.epa.gov/waterscience/basins/
        For original metadata and documentation of source data
        http://nsdi.usgs.gov/nsdi/wais/maps/dem1deg.HTML
  Description:
    Abstract:
      Digital Elevation Model (DEM) is the terminology adopted by
      the USGS to describe terrain elevation data sets in a digital
      raster form.  The standard DEM consists of a regular array of
      elevations cast on a designated coordinate projection system.
      1-degree DEMs (3- by 3-arc second data spacing) provides coverage
      in 1- by 1-degree blocks. The basic elevation model is produced
      by or for the Defense Mapping Agency (DMA), but is distributed
      by the USGS in the DEM data record format. Coverage is for the
      United States.

      The US EPA 1-degree DEM shapefiles are polygonal representations of
      the original USGS DEM raster files resampled to a 300m x 300m cell
      size.  Catolog Units (CU)in each of the ten US EPA Regions were
      buffered by a two mile distance.  The buffered CUs were used to
      clip corresponding areas from the DEM raster files.  The resulting
      files were output in Environmental Systems Research Institute's
      (ESRI) shapefile format.  Two attribute fields were added to
      each shapefile's database component to represent elevation in
      both meters and feet.

    Purpose:
      DEM's can be used as source elevation data for digital orthophotos,
      and, as layers in geographic information systems, for earth science
      analysis. DEM's can also serve as tools for volumetric analysis, for
      site location of towers, or for drainage basin delineation.  The ESRI
      shapefile format allows for analysis involving elevational data and
      also provides for the possibility of contour generation.

    Supplemental_Information:
      One degree DEM's have rows and columns which are based on the 
      geographic  coordinate  system.  The use of this system results
      in a rectangular DEM which shares a common edge and therefore
      duplicate points with other adjacent 1-degree DEM's.

      The original USGS DEMs were downloaded and imported into ArcInfo grid
      format using the demlattice command.  An Arc Macro Language (AML)
      procedure was used to create Arcview shapefiles for each
      CU in the United States.  Processing started with generating a list
      of CUs in an EPA Region and reading the list into ArcInfo.  For each
      CU in the list, an ArcInfo coverage was generated by reselecting all
      polygons associated with the CU from a nationwide CU coverage.
      The individual CU polygon coverage was then buffered with a two mile
      buffer distance.  The buffered coverage was overlayed onto an
      index coverage of 1:250,000 scale DEMs for the United States.  A list
      was generated of all the DEMs that the buffered coverage touched on
      the index.  Each DEM grid coverage in the resulting list was then
      mosaiced into a single grid coverage.  This single grid coverage was
      then projected from a geographic-decimal degrees to an albers-meters
      projection.  The single grid coverage is resampled to a
      300 meter x 300 meter cell size and converted from a raster
      coverage to a vector polygon coverage.  The polygon grid coverage was
      clipped by the buffered CU coverage and projected back to
      geographic-decimal degrees.  Polygons were built for the clipped
      DEM grid coverage and an ArcView shapefile built.  Once the shapefile
      was built, the database component was modified to include fields for
      elevation in both meters and feet.

      Converting the original 1-degree DEMs into ESRI shapefile format
      reduced the number of cells in each DEM coverage by unioning
      adjacent polygons with the same elevation.

      DEM files for Alaska, Puerto Rico, and the U.S. Virgin Islands would
      not initially import into ArcInfo.  ArcInfo versions below 7.1.2
      have a bug in the DEMLATTICE command that incorrectly reads the
      accuracy code found in the first line of the file.  This code
      needs to be changed to 0 from the original codes of either 2231
      or 2232.  The changes were made by changing the block size of
      the file.  The command line for this step is:

      dd if=file.dem of=file.var ibs=4096 cbs=1024 conv=unblock.

      The first line of code was then edited to change the accuracy code.
      This step is done by replacing the each character of 223 with a space
      and the final character of the four digit code with a zero.

      Reviews_Applied_To_Data
      Upon completion of processing, each CU shapefile was viewed in an
      ArcView project to verify the completeness of the datafiles, to look
      for holes in the data, and to look for spikes in the data.
      Individual polygons were measured to verify the 300 meter x 300
      meter cell size.  Additionally, a coverage of all CUs in the US EPA
      Region was drawn on top of the 1-degree DEM shapefiles to verify
      that each CU was processed.

      References_Cited
      U.S. Geological Survey, 1993, Digital Elevation Models-Data Users Guide 5,
      National Mapping Program, USGS, Reston, Virginia
      http://mapping.usgs.gov/pub/ti/DEM/demguide

      U.S. Geological Survey, 1995, Metadata for 1-degree Digital
      Elevation Models.  U.S. Geological Survey, Reston, Virginia.
      http://nsdi.usgs.gov/nsdi/wais/maps/dem1deg.HTML and
      http://edcwww.cr.usgs.gov/glis/hyper/guide/1_dgr_dem

  Time_Period_of_Content:
    Time_Period_Information:
      Range_of_Dates/Times:
        Beginning_Date: 19791000
        Ending_Date: 19900401
    Currentness_Reference: Publication date
  Status:
    Progress: Complete
    Maintenance_and_Update_Frequency: Irregular
  Spatial_Domain:
    Bounding_Coordinates:
      West_Bounding_Coordinate: -170.0000
      East_Bounding_Coordinate: -65.0000
      North_Bounding_Coordinate: 70.0000
      South_Bounding_Coordinate: 17.0000

  Keywords:
    Theme:
      Theme_Keyword_Thesaurus: none
      Theme_Keyword: DEM
      Theme_Keyword: digital elevation model
      Theme_Keyword: digital terrain model
      Theme_Keyword: hypsography
      Theme_Keyword: altitude
      Theme_Keyword: height
      Theme_Keyword: contour line
      Theme_Keyword: digital contours
      Theme_Keyword: shapefile
    Place:
      Place_Keyword_Thesaurus: Geographic Names Information System
      Place_Keyword: Conterminous United States of America
      Place_Keyword: Puerto Rico PR
      Place_Keyword: U.S. Virgin Islands VI
      Place_Keyword: Alabama AL
      Place_Keyword: Alaska AK
      Place_Keyword: Arizona AZ
      Place_Keyword: Arkansas AR
      Place_Keyword: California CA
      Place_Keyword: Colorado CO
      Place_Keyword: Connecticut CT
      Place_Keyword: Delaware DE
      Place_Keyword: District of Columbia DC
      Place_Keyword: Florida FL
      Place_Keyword: Georgia GA
      Place_Keyword: Hawaii HI
      Place_Keyword: Idaho ID
      Place_Keyword: Illinois IL
      Place_Keyword: Indiana IN
      Place_Keyword: Iowa IA
      Place_Keyword: Kansas KS
      Place_Keyword: Kentucky KY
      Place_Keyword: Louisiana LA
      Place_Keyword: Maine ME
      Place_Keyword: Maryland MD
      Place_Keyword: Massachusetts MA
      Place_Keyword: Michigan MI
      Place_Keyword: Minnesota MN
      Place_Keyword: Mississippi MS
      Place_Keyword: Missouri MO
      Place_Keyword: Montana MT
      Place_Keyword: Nebraska NE
      Place_Keyword: Nevada NV
      Place_Keyword: New Hampshire NH
      Place_Keyword: New Jersey NJ
      Place_Keyword: New Mexico NM
      Place_Keyword: New York NY
      Place_Keyword: North Carolina NC
      Place_Keyword: North Dakota ND
      Place_Keyword: Ohio OH
      Place_Keyword: Oklahoma OK
      Place_Keyword: Oregon OR
      Place_Keyword: Pennsylvania PA
      Place_Keyword: Rhode Island RI
      Place_Keyword: South Carolina SC
      Place_Keyword: South Dakota SD
      Place_Keyword: Tennessee TN
      Place_Keyword: Texas TX
      Place_Keyword: Utah UT
      Place_Keyword: Vermont VT
      Place_Keyword: Virginia VA
      Place_Keyword: Washington WA
      Place_Keyword: West Virginia WV
      Place_Keyword: Wisconsin WI
      Place_Keyword: Wyoming WY

  Access_Constraints: None
  Use_Constraints: None

  Security_Information:
    Security_Classification_System: None
    Security_Classification: UNCLASSIFIED
    Security_Handling_Description: None

  Native_Data_Set_Environment: ArcView 3.x shapefiles on Windows 95 PC

Data_Quality_Information:

  Attribute_Accuracy:
    Attribute_Accuracy_Report:
      The accuracy of a DEM is dependent upon the level of
      detail of the source and the grid spacing used to sample
      that source. The primary limiting factor for the level of
      detail of the source is the scale of the source materials.
      The proper selection of grid spacing determines the level
      of content that  may be extracted from a given source
      during digitization.

  Logical_Consistency_Report:
    The fidelity of the relationships encoded in the data
    structure of the DEM are automatically verified using
    a USGS software program upon completion of the data
    production cycle. The test verifies full compliance to the
    DEM specification

  Completeness_Report:
    The DEM is visually inspected for completeness on a DEM view
    and edit system for the purpose of performing a final quality
    control and if necessary edit of the DEM. The physical format
    of each digital elevation model is validated for content
    completeness and logical consistency during production quality
    control and prior to archiving in the National Digital
    Cartographic Data Base.
    Level 2 DEM: Level 2 DEM's may contain void areas due to
    interruptions to contours in the source graphic or DLG. Void area
    elevation grid posts are assigned the value of -32,767. In addition,
    suspect elevation areas may exist in the DEM but are not specifically
    identified. Suspect areas can be located on the source graphic as a
    "disturbed surface" which are symbolized by contours overprinted
    with photorevised or other surface patterns.

  Positional_Accuracy:
    Horizontal_Positional_Accuracy:
      Horizontal_Positional_Accuracy_Report:
        Digital elevation models meet horizontal National Map Accuracy
        Standards (NMAS) accuracy requirements. NMAS horizontal accuracy
        requires that at least 90 percent of points tested are within 0.02
        inches of the true position. The primary reference from which
        1-degree DEM accuracy is derived is source-based, as a minimum,
        meeting NMAS For 100,000-scale USGS topographic series maps.

      Quantitative_Horizontal_Positional_Accuracy_Assessment:
        Horizontal_Positional_Accuracy_Value: 300
        Horizontal_Positional_Accuracy_Explanation:
          Digital elevation models meet horizontal National Map
          Accuracy Standards (NMAS) accuracy requirements.
          RMSE of the DEM.  The 1-degree DEM accuracy is source-dependent
          and is based on the 1:100,000-scale USGS topographic series map.

    Vertical_Positional_Accuracy:
      Vertical_Positional_Accuracy_Report:
        The vertical root-mean-square error (RMSE) statistic is used to
        describe the vertical accuracy of a DEM, encompassing both random
        and systematic errors introduced during production of the data.
        The RMSE is encoded in element number 5 of record C of the DEM.
        Accuracy is computed by a comparison of linear interpolated
        elevations in the DEM with corresponding known elevations.
        Test points are well distributed, representative of the terrain,
        and have true elevations with accuracies well within the DEM
        accuracy criteria.  Acceptable test points include, in order
        of preference: field control, aerotriangulated test points,
        spot elevations, or points on contours from existing source
        maps with appropriate contour interval. A minimum of 28 test
        points per DEM is required to compute the RMSE, which is
        composed of a single test using 20 interior points and 8 edge
        points.  Edge points are those which are located along, at,
        or near the quadrangle neatlines and are deemed by the editor
        to be useful to evaluating the accuracy of the edge of the DEM.
        Collection of test point data and comparison of the DEM with
        the quadrangle hypsography are conducted by the quality control
        units within the USGS.  There are three types of DEM vertical
        error; blunder, systematic and random. These errors are reduced
        in magnitude by editing but cannot be completely eliminated and
        may be encountered.

        Blunder errors are those errors of major proportions and are
        easily identified and removed during interactive editing.
        Systematic errors are those errors that follow some fixed pattern
        and are introduced by data collection procedures and systems.
        These error artifacts include: vertical elevation shifts,
        misinterpretation of terrain surface due to trees, buildings and
        shadows, and fictitious ridges, tops, benches or striations.
        Random errors result from unknown or accidental causes.  DEMs
        are edited to correctly depict elevation surfaces that correspond
        to water bodies of specified size.

        Level 2 DEM: A vertical RMSE of one-half of the contour interval
        (of 100,000-scale source), determined by the source map, is the
        maximum permitted. Systematic errors may not exceed one contour
        interval, determined by the source map, is the maximum permitted.
        Systematic errors may not exceed one contour interval specified
        by the source graphic.  Level 2 DEM's have been processed or
        smoothed for consistency and edited to remove identifiable
        systematic errors.

  Lineage:

    Process_Step:
      Process_Description:
        Example of the GIS process for the DEM convertion to shapefiles

        PROJECT COVER DEMCLIPPED OUTCOV
        BUILD OUTCOV POLY
        IMPORT COVER outcov.E00 outcov
      Process_Date: 20070611

Spatial_Reference_Information:

  Horizontal_Coordinate_System_Definition:
    Geographic:
      Latitude_Resolution: 0.0001
      Longitude_Resolution: 0.0001
      Geographic_Coordinate_Units: Decimal Degrees
    Geodetic_Model:
      Horizontal_Datum_Name: North American Datum of 1983
      Ellipsoid_Name: Geodetic Reference System 80
      Semi-major_Axis: 6,378,137
      Denominator_of_Flattening_Ratio: 298.257
  Vertical_Coordinate_System_Definition:
    Altitude_System_Definition:
      Altitude_Datum_Name: National Geodetic Vertical Datum of 1929
      Altitude_Resolution: 1
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method:  
          Explicit elevation coordinate included with horizontal coordinates

Entity_and_Attribute_Information:

  Detailed_Description:
    Entity_Type:
      Entity_Type_Label: DEM.SHP
      Entity_Type_Definition: DEM shapefile
      Entity_Type_Definition_Source: USEPA/OW
    Attribute:
      Attribute_Label: ELEV_M
      Attribute_Definition: Elevation in meters
      Attribute_Definition_Source: Generated during ArcInfo processing
      Attribute_Domain_Values:
        Enumerated_Domain:
          Enumerated_Domain_Value: Integer
          Enumerated_Domain_Value_Definition: 8 11 F 0
          Enumerated_Domain_Value_Definition_Source: USEPA/OW
    Attribute:
      Attribute_Label: ELEV_FT
      Attribute_Definition: Elevation in feet
      Attribute_Definition_Source: Generated during ArcInfo processing
      Attribute_Domain_Values:
        Enumerated_Domain:
          Enumerated_Domain_Value: Integer
          Enumerated_Domain_Value_Definition: 8 11 F 0
          Enumerated_Domain_Value_Definition_Source: USEPA/OW

Distribution_Information:

  Distributor:
    Contact_Information:
      Contact_Organization_Primary:
        Contact_Organization: USEPA Office of Water/OST Basins
      Contact_Address:
        Address_Type: mailing address
        Address: 1200 Pennsylvania Ave., NW (4305T)
        City: Washington
        State_or_Province: District of Columbia
        Postal_Code: 20460
      Contact_Voice_Telephone: 202-566-0400
      Contact_Facsimile_Telephone: 202-566-0409
      Contact_Electronic_Mail_Address: basins@epa.gov
      Hours_of_Service: 9-3 EST
  Distribution_Liability:
    Although these data have been processed successfully on a
    computer system under contract to the U.S. Environmental Protection
    Agency (USEPA), no warranty expressed or implied is
    made by the USEPA regarding the utility of the data
    on any other system, nor shall the act of distribution
    constitute any such warranty.  The USEPA will warrant
    the delivery of this product in computer-readable format.

  Standard_Order_Process:
    Digital_Form:
      Digital_Transfer_Information:
        Format_Name: Environmental Systems Research Institute (ESRI) ArcView Shapefile
      Digital_Transfer_Option:
        Online_Option:
          Computer_Contact_Information:
            Network_Address:
              Network_Resource_Name: http://www.epa.gov/waterscience/basins/
        Offline_Option:
          Offline_Media: CD-ROM
          Recording_Format: ISO 9660
    Fees: None
    Ordering_Instructions:
      When requesting data by phone or mail, please inquire about spatial data
      sets that work with Better Assessment Science Integrating Point and
      Nonpoint Sources (BASINS).  The BASINS web page has instructions for
      downloading datasets.   It also has a link to The National Center for
      Environmental Publications and Information (NCEPI), from which
      BASINS CD-ROMs may be ordered.  Each CD-ROM contains the BASINS v2.0
      Application and this data set along with others covering the spatial extent
      of an EPA Region.

Metadata_Reference_Information:

  Metadata_Date: 20070611
  Metadata_Contact:
    Contact_Information:
      Contact_Organization_Primary:
        Contact_Organization: USEPA Office of Water/OST/SASD Basins
      Contact_Address:
        Address_Type: mailing address
        Address: 1200 Pennsylvania Ave., NW (4305T)
        City: Washington
        State_or_Province: District of Columbia
        Postal_Code: 20460
      Contact_Voice_Telephone: 202-566-0400
      Contact_Facsimile_Telephone: 202-566-0409
      Contact_Electronic_Mail_Address: basins@epa.gov
  Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata
  Metadata_Standard_Version: 19940608