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Formal metadata: information and software


Metadata in plain language

How does the data set represent geographic features?

  1. How are geographic features stored in the data set?
    Generally you have point locations, a map with lines and polygons, or an image or grid of some sort. Point locations get lumped in with lines and polygons as vector maps. Raster (image or grid) data are handled differently.

    Points or vector maps

    Spatial_Data_Organization_Information:
      Direct_Spatial_Reference_Method: Point or Vector
      Point_and_Vector_Object_Information:
          SDTS_Terms_Description:
            SDTS_Point_and_Vector_Object_Type: Pick from the list below
            Point_and_Vector_Object_Count: How many of these?
          SDTS_Terms_Description:
            SDTS_Point_and_Vector_Object_Type: Another from the list
            Point_and_Vector_Object_Count: How many?
          SDTS_Terms_Description:
            SDTS_Point_and_Vector_Object_Type: More from the list ...
            Point_and_Vector_Object_Count: How many?
    
    The alternative to the SDTS terms is VPF terms; use SDTS terms unless you're working for the Defense Department. Of the 27 different SDTS point and vector object types, the ones you probably want are
    Entity point
    if your data are points that have attributes
    Complete chain
    if your data are arcs
    GT-polygon composed of chains
    if you have built polygon topology

    Raster data (images or grids)

    Spatial_Data_Organization_Information:
      Direct_Spatial_Reference_Method: Raster
      Raster_Object_Information:
          Raster_Object_Type: Point or Pixel or Grid Cell or Voxel
          Row_Count: How many?
          Column_Count: How many?
          Vertical_Count: (use only if your data are 3-D)
    
  2. What coordinate system is used to represent geographic features?
    1. Are your coordinates geographic (latitude and longitude)?
      Spatial_Reference_Information:
        Horizontal_Coordinate_System_Definition:
            Geographic:
              Latitude_Resolution: numerical estimate
              Longitude_Resolution: numerical estimate
              Geographic_Coordinate_Units: Decimal degrees, for example
            Geodetic Model:
              Horizontal_Datum_Name: NAD27 or NAD83
              Ellipsoid_Name: Clarke 1866, for example
              Semi-major_Axis: radius of the earth in kilometers
              Denominator_of_Flattening_Ratio: number, about 300
      
    2. Is this a map with a planar projection?
      Spatial_Reference_Information:
        Horizontal_Coordinate_System_Definition:
            Planar:
              Map_Projection:
                Map_Projection_Name:  projection name from following list:
                  Albers Conical Equal Area
                  Azimuthal Equidistant
                  Equidistant Conic
                  Equirectangular
                  General Vertical Near-sided Projection
                  Gnomonic
                  Lambert Azimuthal Equal Area
                  Lambert Conformal Conic
                  Mercator
                  Modified Stereographic for Alaska
                  Miller Cylindrical
                  Oblique Mercator
                  Orthographic
                  Polar Stereographic
                  Polyconic
                  Robinson
                  Sinusoidal
                  Space Oblique Mercator
                  Stereographic
                  Transverse Mercator
                  van der Grinten
                  other projection
                  
      

      Projection parameters

      Projection parameters need to be specified. These vary from projection to projection, and as the jargon is daunting, this is not a fit topic for a document purporting to explain metadata in plain language.
            Geodetic Model:
              Horizontal_Datum_Name: NAD27 or NAD83
              Ellipsoid_Name: Clarke 1866, for example
              Semi-major_Axis: radius of the earth in kilometers
              Denominator_of_Flattening_Ratio: number, about 300
      


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