Spatial Information

Element Description

Note: this wiki page is a draft/ work in progress

The Spatial Information element stores the reference frame or system from which horizontal and vertical spatial domains are measured. The horizontal reference frame includes a Geodetic Model, Geographic Coordinates, and Local Coordinates. The Vertical reference frame includes altitudes (elevations) and depths.

Best Practices

Providing Spatial Information is optional, but encouraged. This element can be used to provide horizontal and/or vertical coordinate system information. 

If coordinate system information is provided, then the Spatial Coverage Type field is required. This field is used to specify whether the spatial coverage of the collection is horizontal, vertical, horizontal and vertical, orbital, or orbital and vertical.

• Spatial Coverage Type: Denotes the type of spatial coverage of the collection. While this field is not currently controlled, recommend providing one of the spatial coverage type enumeration values: HORIZONTAL, VERTICAL, ORBITAL, HORIZONTAL_VERTICAL, ORBITAL_VERTICAL
  
  

Horizontal Spatial Information

The following sub-elements can be used to describe Horizontal Coordinate Systems.

There are 3 categories for Horizontal Coordinate Systems including:

(1) Geodetic Model

Geodetic Model is used to describe data that has been georeferenced to a datum, which is a well defined ellipsoidal/spherical representation of the Earth. There are many different standard datums. Knowing which datum the data is encoded in is extremely useful for manipulating the data using GIS software. Sub-elements under Geodetic Model are summarized below:

• • • Horizontal Datum Name: The name of the datum the data are encoded in. Also commonly referred to as a geodetic datum. A geodetic datum is a more localized/ specialized version of a simple Ellipsoid model of the Earth (see below). It is recommended that EPSG Datum names be used. 
    • Ellipsoid Name: An elliptical or spherical shape representing the Earth. An Ellipsoid's shape can be defined by a major axis (longer axis) and a minor axis (shorter axis). There are standard names for different Ellipsoids - it is recommended that EPSG Ellipsoid names be used. 
    • Semi Major Axis: The radius of the major axis of the Ellipsoid. The length and units of the Semi Major Axis should be defined in the Ellipsoid standard. 
      
    • Denominator Of Flattening Ratio: The ratio of the Ellipsoid's major axis to the difference between the major and the minor axis. Also referred to as the Inverse Flattening ratio. The smaller the ratio, the 'flatter' or more oval-like the Ellipsoid's shape will be. The units of the Inverse Flattening ratio are also defined by the Ellipsoid standard. 

(2) Geographic Coordinate System

Data that has been georeferenced to a geodetic datum are provided in latitude and longitude coordinates. The Geographic Coordinate System fields can be used to describe the coordinate system in more detail. Sub-elements under Geographic Coordinate System are summarized below:

• • • Geographic Coordinate Units: Units of measure used for the geodetic latitude and longitude resolution values (e.g., decimal degrees or degrees minutes seconds).
    • Latitude Resolution: The minimum difference between two adjacent latitude values in the Geographic Coordinate System, expressed in the Geographic Coordinate Units of measure, expressed as a two-digit decimal number, e.g., 0.01.
    • Longitude Resolution: The minimum difference between two adjacent longitude values in the Geographic Coordinate System, expressed in the Geographic Coordinate Units of measure, expressed as a two-digit decimal number, e.g., 0.01.

(3) Local Coordinate System

Data collected over small or localized areas may be georeferenced to a custom or highly specialized reference system. In order to accurately compare the local data to other data, the local coordinates must be converted to a standard reference system such as one of the EPSG geodetic datums. The Local Coordinate System fields provide information about the local coordinate system. Sub-elements under Local Coordinate System are summarized below:

• • • Geo Reference Information: Information on how the local system were registered to a standard reference system (e.g. control points, satellite ephemeral data, and inertial navigation data). In some cases, the user may be responsible for georeferencing the data.
    • Description: A description of the Local Coordinate System and georeference information.
      
      

Vertical Spatial Information

The following sub-elements can be used to describe Vertical Coordinate Systems.

There are 2 categories for Vertical Coordinate Systems including:

(1) Altitude System Definition 

Altitude System Definition should be used to describe data with a vertical component that is above-ground. Sub-elements under Altitude System Definition are summarized below:

• • • Datum Name: The name of the vertical datum the data is encoded in. Vertical datums define a level reference surface from which vertical measurements are compared. There are many standard vertical datums. If a standard vertical datum is used, it is recommended that the EPSG vertical datum name be provided. 
    • Distance Units: The units in which altitude measurements are recorded.
    • Encoding Method: 
    • Resolutions: The minimum distance possible between two adjacent values, expressed in distance units of measure for the collection.
      

(2) Depth System Definition

Depth System Definition should be used to describe data with a vertical component that is below-ground. Sub-elements under Depth System Definition are summarized below:

• • • Datum Name: The identification given to the level surface taken as the surface of reference from which measurements are compared.
      
    • Distance Units: The units in which measurements are recorded.
    • Encoding Method:
    • Resolutions: The minimum distance possible between two adjacent values, expressed in distance units of measure for the collection.

          Examples:

           SpatialCoverageType: "Horizontal"

           VerticalCoordinateSystem/AltitudeSystemDefinition/DatumName: North American Vertical Datum of 1988

           VerticalCoordinateSystem/AltitudeSystemDefinition/DistanceUnits: "Kilometers"

           VerticalCoordinateSystem/AltitudeSystemDefinition/EncodingMethod: "Implicit coordinate"

           HorizontalCoordinateSystem/LocalCoordinateSystem/GeoReferenceInformation: "Control Points"

           VerticalCoordinateSystem/DepthSystemDefinition/DistanceUnits: "HectoPascals"

Metadata Validation and QA/QC

All metadata entering the CMR goes through the below process to ensure metadata quality requirements are met. All records undergo CMR validation before entering the system. The process of QA/QC is slightly different for NASA and non-NASA data providers. Non-NASA providers include interagency and international data providers and are referred to as the International Directory Network (IDN).

Please see the expandable sections below for flowchart details.

Dialect Mappings

UMM Migration

Future Mappings

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History

UMM Versioning

ARC Documentation