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4. Spatial Reference
Spatial Reference provides the description of the reference frame for, and the means to encode coordinates in a data set. This section contains definitions and examples for the following metadata elements.
Horizontal Coordinate System Definition
Vertical Coordinate System Definition
Horizontal Coordinate System Definition
Horizontal Coordinate System Definition describes the reference frame or system from which linear or angular quantities are measured and assigned to the position that a point occupies. This metadata element encompasses the following sub-elements.
Geographic
The quantities of latitude and longitude which define the position of a point on the Earth's surface with respect to a reference spheroid.
Latitude Resolution
Format: Latitude Resolution > 0.0
Longitude Resolution
Format: Longitude Resolution > 0.0
Geographic Coordinate Units
Format: Select from the following list.
Geographic Coordinate Units:
Decimal degrees
Decimal minutes
Decimal seconds
Degrees and decimal minutes
Degrees, minutes, and decimal seconds
Radians
Grads
Planar
the quantities of distances, or distances and angles, which define the position of a point on a reference plane to which the surface of the Earth has been projected.
Map Projection
The systematic representation of all or part of the surface of the Earth on a plane or developable surface.
Map Projection Name
Format: Select from the following list.
Map Projections:
Albers Conical Equal Area
Azimuthal Equidistant
Equidistant Conic
Equirectangular
General Vertical Near-sided Perspective
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
Example:
Map Projection Name: Lambert Conformal Conic
Map Projection Parameters
The parameters for a specific map projection, each having a unique mathematical relationship between the Earth and the plane or developable surface.
Each map projection has a specific set of defining parameters. The list below provides a reference for identifying the required parameters and syntax for each map projection.1 Definitions and instructions for completing the metadata for the projection parameters follows this list.
Albers Conical Equal Area
Longitude of Central Meridian:
Latitude of Projection Origin:
False Easting:
False Northing:
Azimuthal Equidistant
Latitude of Projection Origin:
False Easting:
False Northing:
Equidistant Conic
Longitude of Central Meridian:
Latitude of Projection Origin:
False Easting:
False Northing:
Equirectangular
Longitude of Central Meridian:
False Easting:
False Northing:
General Vertical Near-sided Perspective:
Longitude of Projection Center:
Latitude of Projection Center:
False Easting:
False Northing:
Gnomonic
Latitude of Projection Center:
False Easting:
False Northing:
Lambert Azimuthal Equal Area
Latitude of Projection Center:
False Easting:
False Northing:
Lambert Conformal Conic
Longitude of Central Meridian:
Latitude of Projection Origin:
False Easting:
False Northing:
Mercator
Longitude of Central Meridian:
False Easting:
False Northing:
Modified Stereographic for Alaska
False Northing:
Miller Cylindrical
False Easting:
False Northing:
Oblique Mercator
Oblique Line Azimuth
Azimuth Measure Point Longitude:
or
Oblique Line Point
Oblique Line Latitude:
Oblique Line Longitude:
Latitude of Projection Origin:
False Easting:
False Northing:
Orthographic
Latitude of Projection Center:
False Easting:
False Northing:
Polar Stereographic
Standard Parallel:
or
Scale Factor at Projection Origin:
False Easting:
False Northing:
Polyconic
Latitude of Projection Origin:
False Easting:
False Northing:
Robinson
False Easting:
False Northing:
Sinusoidal
False Easting:
False Northing:
Space Oblique Mercator (Landsat)
Path Number:
False Easting:
False Northing:
Stereographic
Latitude of Projection Center:
False Easting:
False Northing:
Transverse Mercator
Longitude of Central Meridian:
Latitude of Projection Origin:
False Easting:
False Northing:
van der Grinten
False Easting:
False Northing:
Standard Parallel
Format: -90.0 <= Standard Parallel <= 90.0
Longitude of Central Meridian
Format: -180.0 <= Longitude of Central Meridian <= 180.0
Latitude of Projection Origin
Format: -90.0 <= Latitude of Projection Origin
False Easting
Format: Free text.
False Northing
Format: Free text.
Scale Factor at Equator
Format: Scale Factor at Equator > 0.0
Height of Perspective Point Above Surface
Format: Height of Perspective Point Above Surface > 0.0
Longitude of Projection Center
Format: -180.0 <= Longitude of Projection Center < 180.0
Latitude of Projection Center
Format: -90.0 <= Latitude of Projection Center <= 90.0
Scale Factor at Center Line
Format: Scale Factor at Center Line > 0.0
Oblique Line Azimuth
The method used to describe the line along which an oblique mercator map projection is centered using the map projection origin and an azimuth.
Azimuthal Angle
Format: 0.0 <= Azimuthal Angle < 360.0
Azimuth Measure Point Longitude
Format: -180.0 <= Azimuth Measure Point Longitude < 180.0
Oblique Line Point
The method used to describe the line along which an oblique mercator map projection is centered using two points near the limits of the mapped region that define the center line.
Oblique Line Latitude
Format: -90.0 <= Oblique Line Latitude <= 90.0
Oblique Line Longitude
Format: -180.0 <= Oblique Line Longitude < 180.0
Straight Vertical Longitude from Pole
Format: -180.0 <= Straight Vertical Longitude from Pole < 180.0
Scale Factor at Projection Origin
Format: Scale Factor at Projection Origin > 0.0
Landsat Number
(Note: This data element exists solely to provide a parameter needed to define the space oblique mercator projection. It is not used to identify data originating from a remote sensing vehicle.
Format: 0 < Landsat Number < 5
Path Number
(Note: This data element exists solely to provide a parameter needed to define the space oblique mercator projection. It is not used to identify data originating from a remote sensing vehicle.
Format: 0 < Path Number < 251 for Landsats 1, 2, or 3
0 < Path Number < 233 for Landsats 4 or 5
Scale Factor at Central Meridian
Format: Scale Factor at Central Meridian > 0.0
Other Projection
Format: Free text.
Grid Coordinate System
A plane-rectangular coordinate system usually based on, and mathematically adjusted to, a map projection so that geographic positions can be readily transformed to and from plane coordinates.
Grid Coordinate System Name
Format: Select from the following list.
Grid Coord. System:
Universal Polar Stereographic
State Plane Coordinate System 1927
State Plane Coordinate System 1983
ARC Coordinate System
other grid system
Grid Coordinate System Parameters
Assemble the parameters for the grid system according to the following list. Definitions and instructions for completing the metadata for the Grid Coordinate System follows this list.
Universal Transverse Mercator
Transverse Mercator:
(use parameters from Transverse Mercator)
Polar Stereographic:
(use parameters from Polar Stereographic)
Equirectangular
or
Azimuthal Equidistant
(use parameters from the appropriate projection)
Lambert Conformal Conic
or
Transverse Mercator
or
Oblique Mercator
or
Polyconic
(use parameters from the appropriate projection)
Universal Transverse Mercator (UTM)
A grid system based on the transverse mercator projection, applied between latitudes 84 degrees north and 80 degrees south on the Earth's surface.
UTM Zone Number
Format: Integer; 1 <= UTM Zone Number <= 60 for the northern hemisphere; -60 <= UTM Zone Number <= -1 for the southern hemisphere.
Universal Polar Stereographic (UPS)
A grid system based on the polar stereographic projection, applied to the Earth's polar regions north of 84 degrees north and south of 80 degrees south.
UPS Zone Identifier
Format: A, B, Y, Z
State Plane Coordinate System (SPCS)
A plane-rectangular coordinate system established for each state in the United States by the National Geodetic Survey.
SPCS Zone Identifier
Format: Four digit numeric codes for the State Plane Coordinate Systems based on the North American Datum of 1927 are found in:
U.S. Department of Commerce. 1986. Representation of Geographic Point Locations for Information Interchange. (Federal Information Processing Standard 70-1). Washington, D.C.: U. S. Department of Commerce, National Institute of Standards and Technology.
Codes for the State Plane Coordinate Systems based on the North American Datum of 1983 are found in: U.S. Department of Commerce. 1989 (January). State Plane Coordinate System of 1983. (National Oceanic and Atmospheric Administration Manual NOS NGS 5). Silver Spring, Maryland: National Oceanic and Atmospheric Administration, National Ocean Service, Coast and Geodetic Survey.
ARC Coordinate System
The Equal ARC-second Coordinate System, a plane-rectangular coordinate system established in: U.S. Department of Defense. 1990. Military Specification ARC Digitized Raster Graphics (ADRG). (MIL-A-89007). Philadelphia: U. S. Department of Defense, Defense Printing Service Detachment Office.
ARC System Zone Identifier
Format: Integer: 1 <= ARC System Zone Identifier <= 18
Other Grid System
Format: Free text.
Local Planar
Any right-handed planar coordinate system of which the z-axis coincides with a plumb line through the origin that locally is aligned with the surface of the Earth.
"A local planar coordinate system is any planar coordinate system for which the relationship between the planar coordinates and geographic (latitude and longitude) coordinates is not known. In these cases, the standards ask the producer to describe the coordinate system (the orientation of the axis, etc.) and any means that can be used to link the local system to geographic coordinates."2
Local Planar Description
Format: Free text.
Local Planar Georeference Information
Format: Free text.
Planar Coordinate Information
Information about the coordinate system developed on the planar surface.
Planar Coordinate Encoding Method
Format: Select from list: coordinate pair, distance and bearing, row and column.
Coordinate Representation
The method of encoding the position of a point by measuring its distance from perpendicular reference axes (the "coordinate pair" and "row and column" methods).
Abscissa Resolution
Format: Abscissa Resolution > 0.0
Ordinate Resolution
Format: Ordinate Resolution > 0.0
Distance and Bearing Representation
A method of encoding the position of a point by measuring its distance and direction (azimuthal angle) from another point.
Distance Resolution
Format: Distance Resolution > 0.0
Bearing Resolution
Format: Bearing Resolution > 0.0
Bearing Units
Format: Select from the following list.
Bearing Units:
decimal minutes
decimal seconds
degrees and decimal minutes
degrees, minutes, and decimal seconds
radians
grads
Example:
Bearing Units: degrees and decimal minutes
Bearing Reference Direction
Format: Select from list: North, South
Example:
Bearing Reference Direction: South
Bearing Reference Meridian
Format: Select from list: assumed, grid, magnetic, astronomic, geodetic
Example:
Bearing Reference Meridian: geodetic
Planar Distance Units
Format: Select from list: meters, international feet, survey feet; or free text.
Local Coordinate System
A description of any coordinate system that is not aligned with the surface of the Earth.
"A local coordinate system is any non-planar, non-geographic coordinate system. Examples include oblique photography and unrectified satellite images. In these cases, the standards ask the producer to describe the coordinate system and any means that can be used to link the local system to geographic coordinates."2
Local Description
Format: Free text.
Local Georeference Information
Format: Free text.
Geodetic Model
Parameters for the shape of the Earth.
Horizontal Datum Name
Format: Select: North American Datum of 1927, North American Datum of 1983; or free text.
Ellipsoid Name
Format: Select: Clark 1866, Geodetic Reference System 80; or free text.
Semi-major Axis
Format: Semi-major Axis > 0.0
Denominator of Flattening Ratio
Format: Denominator > 0.0
Vertical Coordinate System Definition
The reference frame or system from which vertical distances (altitudes or depths) are measured. This metadata element encompasses the following sub-elements.
Altitude System Definition
The reference frame or system from which altitudes (elevations) are measured.
Altitude Datum Name
Format: Select: National Geodetic Vertical Datum of 1929, North American Vertical Datum of 1988; or free text.
Altitude Resolution
Format: Altitude Resolution > 0.0
Altitude Distance Units
Format: Select: meters, feet; or free text.
Altitude Encoding Method
Format: Select: Explicit elevation coordinate included with horizontal
coordinates, Implicit coordinate, Attribute values.
Depth System Definition
The reference frame or system from which depths are measured.
Depth Datum Name
Format: Select from the following list; or free text.
Depth Datum:
Chart datum; datum for sounding reduction
Lowest astronomical tide
Highest astronomical tide
Mean low water
Mean high water
Mean sea level
Land survey datum
Mean low water springs
Mean high water springs
Mean low water neap
Mean high water neap
Mean lower low water
Mean lower low water springs
Mean higher high water
Mean higher low water
Mean lower high water
Spring tide
Tropic lower low water
Neap tide
High water
Higher high water
low water
Low-water datum
Lowest low water
Lower low water
Lowest normal low water
Mean tide level
Indian spring low water
High-water full and charge
Low-water full and charge
Columbia River datum
Gulf Coast low water datum
Equatorial springs low water
Approximate lowest astronomical tide
No correction.
Depth Resolution
Format: Depth Resolution > 0.0
Depth Encoding Method
Format: Select: Explicit elevation coordinate included with horizontal
coordinates, Implicit coordinate, Attribute values.
References
1 For reference information on these map projections and their parameters see: Snyder, John. 1987. Map Projections: A Working Manual. U.S. Geological Survey Professional Paper 1395. Washington, D.C: U.S. Government Printing Office.
2 Federal Geographic Data Committee (FGDC). 1995. Content Standards for Digital Geospatial Metadata. Workbook (March 24). Washington, D.C.: FGDC. pp.4-1 - 4-13.
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