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CIESIN's Guide to FGDC Compliant Metadata

4. Spatial Reference Information

Spatial Reference Information is the description of the reference frame for, and the means to encode, coordinates in the dataset.

4. Spatial Reference Information  (Mandatory if Applicable)

CONTAINS:

4.1 Horizontal Coordinate System Definition  (Mandatory if Applicable)
4.2 Vertical Coordinate System Definition  (Mandatory if Applicable)

NOTE: This guide only provides information concerning optionality at the section level and top level elements within each section. Keep in mind that the optionality of a section or compound element always takes precedence over the elements that it contains, and if deemed applicable, then the optionality of its subordinate elements is to be interpreted. Refer to either the FGDC Metadata Workbook, Version 2.0 or Section 4 of the USGS's "Image Map of the Content Standard for Digital Geospatial Metadata", a graphical representation of the Standard for rules concerning optionality.


4.1 Horizontal Coordinate System Definition

Definition: 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 contains the following sub-elements:

4.1.1 Geographic

Definition: The quantities of latitude and longitude which define the position of a point on the Earth's surface with respect to a reference spheroid.

4.1.1.1 Latitude Resolution

Definition: The minimum difference between two adjacent latitude values expressed in Geographic Coordinate Units of measure.

Format: Real; Resolution > 0.0

Example:
Latitude Resolution: 1.0

4.1.1.2 Longitude Resolution

Definition: The minimum difference between two adjacent longitude values expressed in Geographic Coordinate Units of measure.

Format: Real; Resolution > 0.0

Example:
Longitude Resolution: 1.0

4.1.1.3 Geographic Coordinate Units

Definition: Units of measure used for the latitude and longitude values.

Format: Text; Select from list.

Example:
Geographic Coordinate Units: Decimal Degrees
Geographic Coordinate Units
: Decimal Minutes
Geographic Coordinate Units
: Decimal Seconds
Geographic Coordinate Units
: Degrees and Decimal Minutes
Geographic Coordinate Units
: Degrees, Minutes, and Decimal Seconds
Geographic Coordinate Units
: Radians
Geographic Coordinate Units
: Grads

4.1.2 Planar

Definition: 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.

4.1.2.1 Map Projection

Definition: The systematic representation of all or part of the surface of the Earth on a plane or developable surface.

4.1.2.1.1 Map Projection Name

Definition: Name of the map projection.

Format: Free text.

Example:
Map Projection Name
: Albers Conical Equal Area
Map Projection Name
: Azimuthal Equidistant
Map Projection Name
: Equidistant Conic
Map Projection Name
: Equirectangular
Map Projection Name
: General Vertical Near-sided Projection
Map Projection Name
: Gnomonic
Map Projection Name
: Lambert Azimuthal Equal Area
Map Projection Name
: Lambert Conformal Conic
Map Projection Name
: Mercator
Map Projection Name
: Modified Stereographic for Alaska
Map Projection Name
: Miller Cylindrical
Map Projection Name
: Oblique Mercator
Map Projection Name
: Orthographic
Map Projection Name
: Polar Stereographic
Map Projection Name
: Polyconic
Map Projection Name
: Robinson
Map Projection Name
: Sinusoidal
Map Projection Name
: Space Oblique Mercator (Landsat)
Map Projection Name
: Stereographic
Map Projection Name
: Transverse Mercator
Map Projection Name
: Van der Grinten


4.1.2.1.2 Albers Conical Equal Area

Definition: Contains parameters for the Albers Conical Equal Area projection.

4.1.2.1.3 Azimuthal Equidistant

Definition: Contains parameters for the Azimuthal Equidistant projection.

4.1.2.1.4 Equidistant Conic

Definition: Contains parameters for the Equidistant Conic projection.

4.1.2.1.5 Equirectangular

Definition: Contains parameters for the Equirectangular projection.

4.1.2.1.6 General Vertical Near-sided Perspective

Definition: Contains parameters for the General Vertical Near-sided Perspective projection.

4.1.2.1.7 Gnomonic

Definition: Contains parameters for the Gnomonic projection.

4.1.2.1.8 Lambert Azimuthal Equal Area

Definition: Contains parameters for the Lambert Azimuthal Equal Area projection.

4.1.2.1.9 Lambert Conformal Conic

Definition: Contains parameters for the Lambert Conformal Conic projection.

4.1.2.1.10 Mercator

Definition: Contains parameters for the Mercator projection.

4.1.2.1.11 Modified Stereographic for Alaska

Definition: Contains parameters for the Modified Stereographic for Alaska projection.

4.1.2.1.12 Miller Cylindrical

Definition: Contains parameters for the Miller Cylindrical projection.

4.1.2.1.13 Oblique Mercator

Definition: Contains parameters for the Oblique Mercator projection.

4.1.2.1.14 Orthographic

Definition: Contains parameters for the Orthographic projection.

4.1.2.1.15 Polar Stereographic

Definition: Contains parameters for the Polar Stereographic projection.

4.1.2.1.16 Polyconic

Definition: Contains parameters for the Polyconic projection.

4.1.2.1.17 Robinson

Definition: Contains parameters for the Robinson projection.

4.1.2.1.18 Sinusoidal

Definition: Contains parameters for the Sinusoidal projection.

4.1.2.1.19 Space Oblique Mercator (Landsat)

Definition: Contains parameters for the Space Oblique Mercator projection.

4.1.2.1.20 Stereographic

Definition: Contains parameters for the Stereographic projection.

4.1.2.1.21 Transverse Mercator

Definition: Contains parameters for the Transverse Mercator projection.

4.1.2.1.22 Van der Grinten

Definition: Contains parameters for the Van der Grinten projection.

4.1.2.1.23 Map Projection Parameters

Definition: A complete parameter set of the projection that was used for the dataset. The information provided shall include the names of the parameters and values used for the dataset that describe the mathematical relationship between the Earth and the plane or developable surface for the projection.

4.1.2.1.23.1 Standard Parallel

Definition: Line of constant latitude at which the surface of the Earth and the plane or developable surface intersect.

Format: Real; Range from -90.0 to 90.0 latitude.

4.1.2.1.23.2 Longitude of Central Meridian:

Definition: The line of longitude at the center of a map projection generally used as the basis for constructing the projection.

Format: Real; Range from -180.0 to 180.0 longitude.

4.1.2.1.23.3 Latitude of Projection Origin

Definition: Latitude chosen as the origin of rectangular coordinates for a map projection.

Format: Real; Range from -90.0 to 90.0 latitude.

4.1.2.1.23.4 False Easting

Definition: The value added to all "x" values in the rectangular coordinates for a map projection. This value frequently is assigned to eliminate negative numbers and is expressed in the unit of measure identified in Planar Coordinate Units.

Format: Real.

4.1.2.1.23.5 False Northing

Definition: The value added to all "y" values in the rectangular coordinates for a map projection. This value frequently is assigned to eliminate negative numbers and is expressed in the unit of measure identified in Planar Coordinate Units.

Format: Real.

4.1.2.1.23.6 Scale Factor at Equator

Definition: A multiplier for reducing a distance obtained from a map by computation or scaling to the actual distance along the equator.

Format: Real; Factor > 0.0

4.1.2.1.23.7 Height of Perspective Point Above Surface

Definition: Height of viewpoint above the Earth, expressed in meters.

Format: Real; Height > 0.0

4.1.2.1.23.8 Longitude of Projection Center

Definition: Longitude of the point of projection for azimuthal projections.

Format: Real; Range from -180.0 to 180.0 longitude.

4.1.2.1.23.9 Latitude of Projection Center

Definition: Latitude of the point of projection for azimuthal projections.

Format: Real; Range from -90.0 to 90.0 latitude.

4.1.2.1.23.10 Scale Factor at Center Line

Definition: A multiplier for reducing a distance obtained from a map computation or scaling to the actual distance along the center line.

Format: Real; Factor > 0.0

4.1.2.1.23.11 Oblique Line Azimuth

Definition: Method used to describe the line along which an oblique mercator map projection is centered using the map projection origin and an azimuth.

4.1.2.1.23.11.1 Azimuthal Angle

Definition: Angle measured clockwise from north, and expressed in degrees.

Format: Real; Range from 0.0 to 360.0 degrees.

4.1.2.1.23.11.2 Azimuth Measure Point Longitude

Definition: Longitude of the map projection origin.

Format: Real; Range from -180.0 to 180.0 longitude.

4.1.2.1.23.12 Oblique Line Point

Definition: 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.

4.1.2.1.23.12.1 Oblique Line Latitude

Definition: Latitude of a point defining the oblique line.

Format: Real; Range from -90.0 to 90.0 latitude.

4.1.2.1.23.12.2 Oblique Line Longitude

Definition: Longitude of a point defining the oblique line.

Format: Real; Range from -180.0 to 180.0 longitude.

4.1.2.1.23.13 Straight Vertical Longitude from Pole

Definition: Longitude to be oriented straight up from the North or South Pole.

Format: Real; Range from -180.0 to 180.0 longitude.

4.1.2.1.23.14 Scale Factor at Projection Origin

Definition: Multiplier for reducing a distance obtained from a map by computation or scaling to the actual distance at the projection origin.

Format: Real; Factor > 0.0

4.1.2.1.23.15 Landsat Number

Definition: Number of the Landsat satellite. (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: Integer; Range from 1 to 7.

4.1.2.1.23.16 Path Number

Definition: Number of the orbit of the Landsat satellite. (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: Integer; Range from 1 to 251 (Landsat 1, 2, 3) and 1 to 233 (Landsat 4, 5, 7).

4.1.2.1.23.17 Scale Factor at Central Meridian

Definition: A multiplier for reducing a distance obtained from a map by computation or scaling to the actual distance along the central meridian.

Format: Real; Factor > 0.0

4.1.2.1.23.18 Other Projection's Definition

Definition: A complete description of a projection, not described elsewhere in the standard, that was used for the dataset. The information provided shall include the name of the projection, names of the parameters and values used for the dataset, and the citation of the specification for the algorithms that describe the mathematical relationship between Earth and plane or developable surface for the projection.

Format: Free text.

4.1.2.2 Grid Coordinate System

Definition: 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.

4.1.2.2.1 Grid Coordinate System Name

Definition: Name of the grid coordinate system.

Format: Text; Select from list.

Example:
Grid Coordinate System Name
: Universal Transverse Mercator
Grid Coordinate System Name
: Universal Polar Stereographic
Grid Coordinate System Name
: State Plane Coordinate System 1927
Grid Coordinate System Name
: State Plane Coordinate System 1983
Grid Coordinate System Name
: ARC Coordinate System
Grid Coordinate System Name
: Other Grid System

4.1.2.2.2 Universal Transverse Mercator (UTM)

Definition: A grid system based on the transverse mercator projection, applied between latitudes 84 degrees North and 80 degrees South on the Earth's surface.

4.1.2.2.2.1 UTM Zone Number

Definition: Identifier for the UTM zone.

Format: Integer; Range from 1 to 60 (Northern Hemisphere) and -1 to -60 (Southern Hemisphere).

4.1.2.2.3 Universal Polar Stereographic (UPS)

Definition: 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.

4.1.2.2.3.1 UPS Zone Identifier

Definition: Identifier for the UPS zone.

Format: Text; Select from list.

Example:
UPS Zone Identifier
: A
UPS Zone Identifier
: B
UPS Zone Identifier
: Y
UPS Zone Identifier
: Z

4.1.2.2.4 State Plane Coordinate System

Definition: A plane-rectangular coordinate system established for each state in the United States by the National Geodetic Survey.

4.1.2.2.4.1 SPCS Zone Identifier

Definition: Identifier for the SPCS zone.

Format: Text; Four-digit numeric codes for the State Plane Coordinate Systems based on the North American Datum of 19271 and codes for the State Plane Coordinate Systems based on the North American Datum of 19832.

4.1.2.2.5 ARC Coordinate System

Definition: The Equal Arc-second Coordinate System, a plane-rectangular coordinate system3.

4.1.2.2.5.1 ARC System Zone Identifier

Definition: Identifier for the ARC Coordinate System zone.

Format: Integer; Range from 1 to 18.

4.1.2.2.6 Other Grid System's Definition

Definition: A complete description of a grid system, not defined elsewhere in this standard, that was used for the dataset. The information provided shall include the name of the grid system, the names of the parameters and values used for the dataset, and the citation of the specification for the algorithms that describe the mathematical relationship between the Earth and the coordinates of the grid system.

Format: Free text.

4.1.2.3 Local Planar

Definition: 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."4

4.1.2.3.1 Local Planar Description

Definition: A description of the local planar system.

Format: Free text.

4.1.2.3.2 Local Planar Georeference Information

Definition: A description of the information provided to register the local planar system to the Earth (e.g. control points, satellite ephemeral data, inertial navigation data).

Format: Free text.

4.1.2.4 Planar Coordinate Information

Definition: Information about the coordinate system developed on the planar surface.

4.1.2.4.1 Planar Coordinate Encoding Method

Definition: The means used to represent horizontal positions.

Format: Text; Select from list.

Example:
Planar Coordinate Encoding Method
: Coordinate Pair
Planar Coordinate Encoding Method
: Distance and Bearing
Planar Coordinate Encoding Method
: Row and Column

4.1.2.4.2 Coordinate Representation

Definition: 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).

4.1.2.4.2.1 Abscissa Resolution

Definition: The (nominal) minimum distance between the "x" or column values of two adjacent points, expressed in Planar Distance Units of measure.

Format: Real; Resolution > 0.0

4.1.2.4.2.2 Ordinate Resolution

Definition: The (nominal) minimum distance between the "y" or row values of two adjacent points, expressed in Planar Distance Units of measure.

Format: Real; Resolution > 0.0

4.1.2.4.3 Distance and Bearing Representation

Definition: A method of encoding the position of a point by measuring its distance and direction (azimuthal angle) from another point.

4.1.2.4.3.1 Distance Resolution

Definition: The minimum distance measurable between two points, expressed in Planar Distance Units of measure.

Format: Real; Resolution > 0.0

4.1.2.4.3.2 Bearing Resolution

Definition: The minimum angle measurable between two points, expressed in Bearing Units of measure.

Format: Real; Resolution > 0.0

4.1.2.4.3.3 Bearing Units

Definition: Units of measure used for angles.

Format: Text; Select from list.

Example:
Bearing Units
: Decimal Degrees
Bearing Units
: Decimal Minutes
Bearing Units
: Decimal Seconds
Bearing Units
: Degrees and Decimal Minutes
Bearing Units
: Degrees, Minutes, and Decimal Seconds
Bearing Units
: Radians
Bearing Units
: Grads

4.1.2.4.3.4 Bearing Reference Direction

Definition: Direction from which the bearing is measured.

Format: Text; Select from list.

Example:
Bearing Reference Direction
: North
Bearing Reference Direction
: South

4.1.2.4.3.5 Bearing Reference Meridian

Definition: Axis from which the bearing is measured.

Format: Text; Select from list.

Example:
Bearing Reference Meridian
: Assumed
Bearing Reference Meridian
: Grid
Bearing Reference Meridian
: Magnetic
Bearing Reference Meridian
: Astronomic
Bearing Reference Meridian
: Geodetic

4.1.2.4.4 Planar Distance Units

Definition: Units of measure used for distances.

Format: Free text.

Example:
Planar Distance Units
: Meters
Planar Distance Units
: International Feet
Planar Distance Units
: Survey Feet


4.1.3 Local

Definition: 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."4

4.1.3.1 Local Description

Definition: A description of the coordinate system and its orientation to the surface of the Earth.

Format: Free text.

4.1.3.2 Local Georeference Information

Definition: A description of the information provided to register the local system to the Earth (e.g. control points, satellite ephemeral data, inertial navigation data).

Format: Free text.

4.1.4 Geodetic Model

Definition: Parameters for the shape of the Earth.

4.1.4.1 Horizontal Datum Name

Definition: The identification given to the reference system used for defining the coordinates of points.

Format: Free text.

Example:
Horizontal Datum Name
: North American Datum of 1927
Horizontal Datum Name
: North American Datum of 1983

4.1.4.2 Ellipsoid Name

Definition: Identification given to established representations of the Earth's shape.

Format: Free text.

Example:
Ellipsoid Name
: Clark 1866,
Ellipsoid Name
: Geodetic Reference System 80

4.1.4.3 Semi-major Axis

Definition: Radius of the equatorial axis of the ellipsoid.

Format: Real; Axis > 0.0

4.1.4.4 Denominator of Flattening Ratio

Definition: The denominator of the ratio of the difference between the equatorial and polar radii of the ellipsoid when the numerator is set to 1.

Format: Real; Ratio > 0.0


4.2 Vertical Coordinate System Definition

Definition: The reference frame or system from which vertical distances (altitudes or depths) are measured. This metadata element contains the following sub-elements:

4.2.1 Altitude System Definition

Definition: The reference frame or system from which altitudes (elevations) are measured. The term "altitude"' is used instead of the common term "elevation" to conform to the terminology in Federal Information Processing Standards 70-1 and 173.

4.2.1.1 Altitude Datum Name

Definition: The identification given to the surface taken as the surface of reference from which altitudes are measured.

Format: Free text.

Example:
Altitude Datum Name
: National Geodetic Vertical Datum of 1929
Altitude Datum Name
: North American Vertical Datum of 1988

4.2.1.2 Altitude Resolution

Definition: The minimum distance possible between two adjacent altitude values, expressed in Altitude Distance Units of measure.

Format: Real; Resolution > 0.0

4.2.1.3 Altitude Distance Units

Definition: Units in which altitudes are recorded.

Format: Free text.

Example:
Altitude Distance Units
: Meters
Altitude Distance Units
: Feet

4.2.1.4 Altitude Encoding Method

Definition: The means used to encode the altitudes.

Format: Text; Select from list.

Example:
Altitude Encoding Method
: Explicit elevation coordinate included with horizontal coordinates
Altitude Encoding Method
: Implicit coordinate
Altitude Encoding Method
: Attribute values

4.2.2 Depth System Definition

Definition: The reference frame or system from which depths are measured.

4.2.2.1 Depth Datum Name

Definition: The identification given to surface of reference from which depths are measured.

Format: Free text.

Example:
Depth Datum Name
: Local surface
Depth Datum Name
: Chart datum; datum for sounding reduction
Depth Datum Name
: Lowest astronomical tide
Depth Datum Name
: Highest astronomical tide
Depth Datum Name
: Mean low water
Depth Datum Name
: Mean high water
Depth Datum Name
: Mean sea level
Depth Datum Name
: Land survey datum
Depth Datum Name
: Mean low water springs
Depth Datum Name
: Mean high water springs
Depth Datum Name
: Mean low water neap
Depth Datum Name
: Mean high water neap
Depth Datum Name
: Mean lower low water
Depth Datum Name
: Mean lower low water springs
Depth Datum Name
: Mean higher high water
Depth Datum Name
: Mean higher low water
Depth Datum Name
: Mean lower high water
Depth Datum Name
: Spring tide
Depth Datum Name
: Tropic lower low water
Depth Datum Name
: Neap tide
Depth Datum Name
: High water
Depth Datum Name
: Higher high water
Depth Datum Name
: Low water
Depth Datum Name
: Low-water datum
Depth Datum Name
: Lowest low water
Depth Datum Name
: Lower low water
Depth Datum Name
: Lowest normal low water
Depth Datum Name
: Mean tide level
Depth Datum Name
: Indian spring low water
Depth Datum Name
: High-water full and charge
Depth Datum Name
: Low-water full and charge
Depth Datum Name
: Columbia River datum
Depth Datum Name
: Gulf Coast low water datum
Depth Datum Name
: Equatorial springs low water
Depth Datum Name
: Approximate lowest astronomical tide
Depth Datum Name
: No correction

4.2.2.2 Depth Resolution

Definition: The minimum distance possible between two adjacent depth values, expressed in Depth Distance Units of measure.

Format: Real; Resolution > 0.0

4.2.2.3 Depth Distance Units

Definition: Units in which depths are recorded.

Format: Free text.

Example:
Depth Distance Units
: Meters
Depth Distance Units
: Feet

4.2.2.4 Depth Encoding Method

Definition: The means used to encode depths.

Format: Text; Select from list.

Example:
Depth Encoding Method
: Explicit elevation coordinate included with horizontal coordinates
Depth Encoding Method
: Implicit coordinate
Depth Encoding Method
: Attribute values

References

1U.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.

2
U.S. Department of Commerce. 1989. 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.

3
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.

4
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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