CA Projection

All maps in this series are represented in the Albers Equal Area Projection. This information is included in the header file of each geotiff image. The following is the standard text representaiton of the geotiff header:

Example 1. Geotiff Header Information

For California Teale Albers, NAD27 projection:

  Geotiff_Information:
     Version: 1
     Key_Revision: 1.0
     Tagged_Information:
        End_Of_Tags.
     Keyed_Information:
        GTModelTypeGeoKey (Short,1): ModelTypeProjected
        GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
        GeographicTypeGeoKey (Short,1): GCS_NAD27
        ProjectedCSTypeGeoKey (Short,1): User-Defined
        PCSCitationGeoKey (Ascii,38): "Albers Equal Area North American 1927"
        ProjectionGeoKey (Short,1): User-Defined
        ProjCoordTransGeoKey (Short,1): CT_AlbersEqualArea
        ProjLinearUnitsGeoKey (Short,1): Linear_Meter
        ProjStdParallel1GeoKey (Double,1): 34
        ProjStdParallel2GeoKey (Double,1): 40.5
        ProjNatOriginLongGeoKey (Double,1): -120
        ProjNatOriginLatGeoKey (Double,1): 0
        ProjFalseEastingGeoKey (Double,1): 0
        ProjFalseNorthingGeoKey (Double,1): -4000000
        End_Of_Keys.
     End_Of_Geotiff.

For California Teale Albers, NAD83 projection:

Geotiff_Information:
   Version: 1
   Key_Revision: 1.2
   Tagged_Information:
      End_Of_Tags.
   Keyed_Information:
      GTModelTypeGeoKey (Short,1): ModelTypeProjected
      GTRasterTypeGeoKey (Short,1): RasterPixelIsPoint
      GeographicTypeGeoKey (Short,1): GCS_NAD83
      ProjectedCSTypeGeoKey (Short,1): User-Defined
      ProjectionGeoKey (Short,1): User-Defined
      ProjCoordTransGeoKey (Short,1): CT_AlbersEqualArea
      ProjLinearUnitsGeoKey (Short,1): Linear_Meter
      ProjCenterLongGeoKey (Double,1): -120
      ProjNatOriginLatGeoKey (Double,1): 0
      ProjFalseEastingGeoKey (Double,1): 0
      ProjFalseNorthingGeoKey (Double,1): -4000000
      ProjStdParallel1GeoKey (Double,1): 34
      ProjStdParallel2GeoKey (Double,1): 40.5
      PCSCitationGeoKey (Ascii,38): "Albers Equal Area North American 1983"
      ProjectedCSTypeGeoKey (Short,1): User-Defined
      ProjLinearUnitsGeoKey (Short,1): Linear_Meter
      End_Of_Keys.
   End_Of_Geotiff.

The OpenGIS WKS representation of this projection is:

Example 2. OpenGIS WKS Projection Information

For California Teale Albers, NAD27 projection:

  PROJCS["Custom",
         GEOGCS["GCS_North_American_1927",
                DATUM["D_North_American_1927",
                      SPHEROID["Clarke_1866",6378206.4,294.9786982]],
                PRIMEM["Greenwich",0],
                UNIT["Degree",0.0174532925199433]],
         PROJECTION["Albers"],
         PARAMETER["False_Easting",0],
         PARAMETER["False_Northing",-4000000],
         PARAMETER["Central_Meridian",-120],
         PARAMETER["Standard_Parallel_1",34],
         PARAMETER["Standard_Parallel_2",40.5],
         UNIT["Meter",1]]         

For California Teale Albers, NAD83 projection:

  PROJCS["Custom",
         GEOGCS["NAD83",
                DATUM["North_American_Datum_1983",
                      SPHEROID["GRS 1980",6378137,298.257222101]],
                PRIMEM["Greenwich",0],
                UNIT["degree",0.0174532925199433]],
         PROJECTION["Albers"],
         PARAMETER["False_Easting",0],
         PARAMETER["False_Northing",-4000000],
         PARAMETER["Central_Meridian",-120],
         PARAMETER["Standard_Parallel_1",34],
         PARAMETER["Standard_Parallel_2",40.5],
         UNIT["Meter",1]]

The associated proj4 arguments are:

Example 3. Proj 4 parameters

For California Teale Albers, NAD27 projection:

  +proj=aea
  +lat_1=34.00
  +lat_2=40.50
  +lat_0=0.00
  +lon_0=-120.00
  +x_0=0.000 
  +y_0=-4000000.000 
  +ellps=clrk66 
  +units=m 

For California Teale Albers, NAD83 projection:

  +proj=aea 
  +lat_1=34.00 
  +lat_2=40.50 
  +lat_0=0.00 
  +lon_0=-120.00 
  +x_0=0.000 
  +y_0=-4000000.000 
  +ellps=GRS80 
  +units=m 
  +datum=NAD83

The corner coordinates vary with each individual map.