Identification_Information:
  Citation:
    Citation_Information:
      Originator: U.S. Geological Survey
      Publication_Date: 20010920
      Title: 7.5 minute Digital Elevation Model (DEM) for Halifax Quadrangle 10-meter resolution
      Publication_Information:
        Publication_Place: Reston, Virginia
        Publisher: U.S. Geological Survey
      Online_Linkage: ftp://www.pasda.psu.edu/pub/pasda/dem24k_10m/halifax_pa.zip
      Online_Linkage: ftp://www.pasda.psu.edu/pub/pasda/dem24k_10m/halifax_pa.zip
      Larger_Work_Citation:
        Citation_Information:
          Originator: U.S. Geological Survey
          Publication_Date: Unknown
          Title: 7.5 Minute Digital Elevation Models
          Publication_Information:
            Publication_Place: Reston, Virginia
            Publisher: U.S. Geological Survey
          Other_Citation_Details: none
          Online_Linkage: http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.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. The DEM data are stored as a series of
      profiles in which the spacing of the elevations along and between each
      profile is in regular whole number intervals. The normal orientation of
      data is by columns and rows. Each column contains a series of elevations
      ordered from south to north with the order of the columns from west to
      east. The DEM is formatted as one ASCII header record (A-record),
      followed by a series of profile records (B-records) each of which include
      a short B-record header followed by a series of ASCII integer elevations
      per each profile. The last physical record of the DEM is an accuracy record
      (C-record).
      7.5-minute DEM (10- by 10-meter data spacing, cast on Universal Transverse
      Mercator (UTM) projection). Provides coverage in 7.5- by 7.5-minute
      blocks. Each product provides the same coverage as a standard USGS
      7.5-minute quadrangle without over edge. Coverage is for the Contiguous
      United States, Hawaii, and Puerto Rico.
    Purpose:
      DEM's can be used as source 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. These data were collected as
      part of the National Mapping Program.
    Supplemental_Information:
      7.5-minute DEM's have rows and columns which vary in length and are staggered.
      The UTM bounding coordinates form a quadrilateral (no two sides are parallel
      to each other), rather than a rectangle. The user will need to pad out the
      uneven rows and columns with blanks or flagged data values, if a rectangle is
      required for the user's application. Some software vendors have incorporated
      this function into their software for input of standard formatted USGS DEMs.
  Time_Period_of_Content:
    Time_Period_Information:
      Single_Date/Time:
        Calendar_Date: 20010920
    Currentness_Reference: publication date
  Status:
    Progress: Complete
    Maintenance_and_Update_Frequency: Irregular
  Spatial_Domain:
    Bounding_Coordinates:
      West_Bounding_Coordinate: -77
      East_Bounding_Coordinate: -76.875
      North_Bounding_Coordinate: 40.5
      South_Bounding_Coordinate: 40.375
  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: relief
    Place:
      Place_Keyword_Thesaurus: none
      Place_Keyword: Halifax Quadrangle
      Place_Keyword: Pennsylvania
  Access_Constraints: none
  Use_Constraints:
    None. Acknowledgement of the U.S. Geological Survey would
    be appreciated in products derived from these data.
  Point_of_Contact:
    Contact_Information:
      Contact_Organization_Primary:
        Contact_Organization: U.S. Geological Survey
      Contact_Address:
        Address_Type: mailing address
        Address: 508 National Center
        City: Reston
        State_or_Province: VA
        Postal_Code: 22092
      Contact_Voice_Telephone: 1-800 USA MAPS
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.

    Due to the variable orientation of the quadrilateral in relation to the Universal Transverse Mercator (UTM) projection grid, profiles that pass within the bounds of the DEM quadrilateral, may be void of elevation grid points, and are not represented in the DEM. This condition occurs infrequently and is always the first or last profile of the dataset.

    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, " symbolized by contours overprinted with photorevised or other surface patterns.  
  Positional_Accuracy:
    Horizontal_Positional_Accuracy:
      Horizontal_Positional_Accuracy_Report:
        The horizontal accuracy of the DEM is expressed as an estimated root mean square error (RMSE).  The estimate of the RMSE is based upon horizontal accuracy tests of the DEM source materials which are selected as equal to or less than intended horizontal RMSE error of the DEM.
         
        The testing of horizontal accuracy of the source materials isaccomplished by comparing the planimetric (X and Y) coordinates of well-defined  ground points with the coordinates of the same points as determined from a source of higher  accuracy.
    Vertical_Positional_Accuracy:
      Vertical_Positional_Accuracy_Report:
        The vertical 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 errors; blunder, systematic and random.  These errors are reduced in magnitude by editing but cannot be completely eliminated. 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.

        DEM's are edited to correctly depict elevation surfaces that correspond to water bodies of specified size.

        Level 1 DEM: A RMSE of 7-meters or less is the desired accuracy standard. A RMSE of 15-meters is the maximum permitted. A 7.5-minute DEM at this level has an absolute elevation error tolerance of 50 meters (approximately three times the 15-meter RMSE) for blunder errors for any grid node when compared to the true elevation.  Any array of points in the DEM can not encompass more than 49 contiguous elevations in error by more than 21 meters (three times the 7-meter RMSE).  Systematic errors that are within stated accuracy standards are tolerated.

        Level 2 DEM:  A vertical RMSE of one-half of the contour interval, 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 DEMs have been processed or smoothed for consistency and edited to remove identifiable systematic errors.
  Lineage:
    Source_Information:
      Source_Citation:
        Citation_Information:
          Originator: U.S. Geological Survey
          Publication_Date: Unknown
          Title: digital contour lines
          Publication_Information:
            Publication_Place: Reston, Virginia
            Publisher: U.S. Geological Survey
      Type_of_Source_Media: magnetic tape
      Source_Time_Period_of_Content:
        Time_Period_Information:
          Range_of_Dates/Times:
            Beginning_Date: Unknown
            Ending_Date: Present
        Source_Currentness_Reference: ground condition
      Source_Citation_Abbreviation: CONTOUR1
      Source_Contribution: Hypsographic vector information which is interpolated to regular grid posts to form DEM grids in 30- by 30- meter UTM data spacing within the 7.5 minute DEM bounds.
    Source_Information:
      Source_Citation:
        Citation_Information:
          Originator: U.S. Geological Survey
          Publication_Date: Unknown
          Title: ariel photograph ID number
          Geospatial_Data_Presentation_Form: remote-sensing image
          Publication_Information:
            Publication_Place: Reston, Virginia
            Publisher: U.S. Geological Survey
      Type_of_Source_Media: transparency
      Source_Time_Period_of_Content:
        Time_Period_Information:
          Range_of_Dates/Times:
            Beginning_Date: Unknown
            Ending_Date: Present
        Source_Currentness_Reference: ground condition
      Source_Citation_Abbreviation: PHOTO1
      Source_Contribution: elevation values
    Source_Information:
      Source_Citation:
        Citation_Information:
          Originator: U.S. Geological Survey
          Publication_Date: Unknown
          Title: project control
          Geospatial_Data_Presentation_Form: map
          Publication_Information:
            Publication_Place: Reston, Virginia
            Publisher: U.S. Geological Survey
      Type_of_Source_Media: magnetic tape
      Source_Time_Period_of_Content:
        Time_Period_Information:
          Range_of_Dates/Times:
            Beginning_Date: Unknown
            Ending_Date: Present
        Source_Currentness_Reference: ground condition
      Source_Citation_Abbreviation: CONTROL1
      Source_Contribution: ground control points
    Process_Step:
      Process_Description:
        The production procedures, instrumentation, hardware
        and software used in the collection of standard U.S. Geological Survey
        Digital Elevation Models (DEM's) vary depending on systems used at the
        contractor, cooperator or National Mapping Division (NMD) production
        sites. This process step describes, in general, the process used in the
        production of standard USGS DEM datasets.
        Level 1 DEM: Level 1 DEM's are acquired photogrammetrically by manual
        profiling or image correlation techniques from National Aerial Photography
        Program (NAPP) or equivalent source photographs. Level 1 30-minute DEM's
        may be derived or resampled from level 1 7.5-minute DEM's.
        Level 2 DEM: Level 2 DEM's are produced by converting 1:24,000-scale and
        1:100,000-scale hypsography digital line graph (DLG) data to DEM format
        or the DEM's are generated from vector data derived from scanned raster
        files of USGS 1:24,000-scale or 1:100,000-scale map series contour
        separates.
        Level 3 DEM: Level 3 DEM's are created from DLG data that has been
        vertically integrated with all categories of hypsography, hydrography,
        ridge line, break line, drain files and all vertical and horizontal control
        networks. The production of level 3 DEM's requires a system of logic
        incorporated into the software interpolation algorithms that clearly
        differentiates and correctly interpolates between the various types of
        terrain, data densities and data distribution.
        Water Body Editing: DEM surface areas corresponding to water bodies are
        flattened and assigned map specified or estimated surface elevations. Water
        body areas are defined as ponds, lakes, and reservoirs that exceed 0.5
        inches at map scale and double line drainage that exceeds 0.25 inches at
        map scale. Water body shorelines are derived either from a hypsographic DLG
        or by interactive delineation from 1:24,000-scale or 1:100,000-scale USGS
        map series.
        Edge Matching: DEM datasets within a project area (consisting of a number
        of adjacent files) are edge matched to assure terrain surface continuity
        between files. Edge matching is the process of correcting adjacent
        elevation values along common edges. The objective of edge matching is to
        create more accurate terrain representations by correcting the alignment of
        ridges and drains, and overall topographic shaping within an approximately
        25-30 row or column grid post zone on both edges.
        Quality Control: DEM's are viewed on interactive editing systems to
        identify and correct blunder and systematic errors. DEM's are verified for
        physical format and logical consistency at the production centers and
        before archiving in the National Digital Cartographic Data Base (NDCDB)
        utilizing the Digital Elevation Model Verification System (DVS) software.
      Source_Used_Citation_Abbreviation: CONTOUR1, PHOTO1, CONTROL1
      Process_Date: Unknown
Spatial_Data_Organization_Information:
  Direct_Spatial_Reference_Method: raster
  Raster_Object_Information:
    Raster_Object_Type: grid cell
Spatial_Reference_Information:
  Horizontal_Coordinate_System_Definition:
    Planar:
      Grid_Coordinate_System:
        Grid_Coordinate_System_Name: Universal Transverse Mercator
        Universal_Transverse_Mercator:
          UTM_Zone_Number: 18
          Transverse_Mercator:
            Scale_Factor_at_Central_Meridian: .9996
            Longitude_of_Central_Meridian: -123.000
            Latitude_of_Projection_Origin: 0.0
            False_Easting: 500000
            False_Northing: 0.0
      Planar_Coordinate_Information:
        Planar_Coordinate_Encoding_Method: row and column
        Coordinate_Representation:
          Abscissa_Resolution: 10
          Ordinate_Resolution: 10
        Planar_Distance_Units: meters
    Geodetic_Model:
      Horizontal_Datum_Name: North American Datum of 1927
      Semi-major_Axis: 6378206.4
      Denominator_of_Flattening_Ratio: 294.9787
  Vertical_Coordinate_System_Definition:
    Altitude_System_Definition:
      Altitude_Datum_Name: National Geodetic Vertical Datum of 1929
      Altitude_Resolution: .001
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method: Explicit elevation coordinate included with horizontal coordinates
Entity_and_Attribute_Information:
  Overview_Description:
    Entity_and_Attribute_Overview:
      The digital elevation model is composed of a 6-character integer raster representing a gridded
      form of a topographic map hypsography overlay. Each raster entity contains a 6-character integer value
      between -32,767 to 32,768.
    Entity_and_Attribute_Detail_Citation:
      U.S.Department of the Interior, U.S. Geological Survey, Digital Elevation Models -- Data Users Guide; Reston, VA,

      A hypertext extract is available at: URL: http://edcwww.cr.usgs.gov/glis/hyper/guide/usgs_dem

      Softcopies in ASCII and WordPerfect format are available at: URL: ftp://mapping.usgs.gov/pub/ti/DEM/

      U.S.Department of the Interior, U.S. Geological Survey, 1992, Standards for digital elevation models: Reston, VA,

      Softcopies in ASCII and WordPerfect format are available at: URL: ftp://mapping.usgs.gov/pub/ti/DEM/ 
Distribution_Information:
  Distributor:
    Contact_Information:
      Contact_Organization_Primary:
        Contact_Organization: Pennsylvania Spatial Data Access (PASDA)
      Contact_Address:
        Address_Type: mailing address
        Address: Land and Water Building
        City: University Park
        State_or_Province: PA
        Postal_Code: 16802
        Country: USA
      Contact_Electronic_Mail_Address: pasda@psu.edu
  Distribution_Liability: The USER shall indemnify, save harmless, and, if requested, defend those parties involved with the development and distribution of this data, their officers, agents, and employees from and against any suits, claims, or actions for injury, death, or property damage arising out of the use of or any defect in the FILES or any accompanying documentation. Those parties involved with the development and distribution excluded any and all implied warranties, including warranties or merchantability and fitness for a particular purpose and makes no warranty or representation, either express or implied, with respect to the FILES or accompanying documentation, including its quality, performance, merchantability, or fitness for a particular purpose. The FILES and documentation are provided "as is" and the USER assumes the entire risk as to its quality and performance. Those parties involved with the development and distribution of this data will not be liable for any direct, indirect, special, incidental, or consequential damages arising out of the use or inability to use the FILES or any accompanying documentation.
  Standard_Order_Process:
    Digital_Form:
      Digital_Transfer_Information:
        Format_Name: DEM
        File_Decompression_Technique: zip
        Format_Information_Content: USGS standard DEM: The standard USGS DEM can be described as an ASCII formatted elevation file preceded by a metadata header file which consists of one 1024 byte ACSII record as .txt file.  Archive also contains full FGDC metadata in text, HTML and XML format.
        Transfer_Size: 1-2.7 MB
      Digital_Transfer_Option:
        Online_Option:
          Computer_Contact_Information:
            Network_Address:
              Network_Resource_Name: ftp://www.pasda.psu.edu/pub/pasda/dem24k_10m/halifax_pa.zip
Distribution_Information:
  Distributor:
    Contact_Information:
      Contact_Organization_Primary:
        Contact_Organization: Earth Science Information Center, U.S. Geological Survey
      Contact_Address:
        Address_Type: mailing address
        Address: 507 National Center
        City: Reston
        State_or_Province: VA
        Postal_Code: 22092
      Contact_Voice_Telephone: 1-800 USA MAPS
      Contact_Instructions:
        In addition to the address above there are other ESIC
        offices throughout the country.  A full list of these offices is at:  URL
        http://www-nmd.usgs.gov/esic/esic_index.html
    Distribution_Liability:
      Although these data have been processed
      successfully on a computer system at the U.S. Geological Survey, no
      warranty expressed or implied is made by the Geological Survey regarding
      the utility of the data on any other system, nor shall the act of
      distribution constitute any such warranty. 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 adjustments of credit must be
      made within 90 days from the date of this shipment from the ordering date.
  Standard_Order_Process:
    Digital_Form:
      Digital_Transfer_Information:
        Format_Name: DEM
        File_Decompression_Technique: ZIP
        Format_Information_Content:
          USGS standard DEM:  The standard USGS DEM can be described as an ASCII formatted elevation file preceded by a metadata
          header file which consists of one 1024 byte ACSII record.
      Digital_Transfer_Option:
        Online_Option:
          Computer_Contact_Information:
            Network_Address:
              Network_Resource_Name: http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html
    Fees: none
Metadata_Reference_Information:
  Metadata_Date: 20030405
  Metadata_Contact:
    Contact_Information:
      Contact_Organization_Primary:
        Contact_Organization: Pennsylvania Spatial Data Access (PASDA)
      Contact_Position: Metadata Coordinator
      Contact_Address:
        Address_Type: mailing address
        Address: 115 Land and Water Building
        City: University Park
        State_or_Province: PA
        Postal_Code: 16802
        Country: USA
      Contact_Voice_Telephone: 814-865-8792
      Contact_Facsimile_Telephone: 814-865-3378
      Contact_Electronic_Mail_Address: cxp7@psu.edu
  Metadata_Standard_Name: Content Standards for Digital Geospatial Metadata
  Metadata_Standard_Version: FGDC-STD-001-1998
