I need to define the spatial, temporal, and vertical extents of resources associated with my metadata.

Overview

The ISO EX_Extent object is used to describe the spatial, temporal and vertical extent of resources, responsibilities, processing, quality reports, or maintenance.

The EX_Extent object supports multiple geographic and temporal extents within a single object.  This capability is quite useful for describing datasets created from observations collected at different locations and times.  For example, a dataset that includes observations collected at different locations each field season.

Recommendations for ISO 19115 and 19115-1

Bounding Extent. The ISO metadata standards allow multiple extents to be associated with a resource. This capability can be very important as spatial and temporal observatory deployments become more complex. Many metadata tools require a single bounding extent in order to support simple spatial and temporal discovery. In order to easily and unambiguously identify the bounding extent for a resource, we recommend identifying it with an xml id = 'boundingExtent'.

Two-Dimensional Tiling Systems. Several NASA metadata standards include the capability to describe spatial extents of resources using two-dimensional tiling systems. The tile numbers in these systems are standard geographic identifiers that can be used to improve performance of spatial searches. MENDS recommended syntax for these tile identifiers in ISO.

Conceptual Model (UML)

XML Example - Bounding Extent

 This example describes a simple spatial and temporal extent for a dataset that extends to the present. It includes ids (boundingExtent, boundingBox, and boundingTime) that allow the bounding extents to be referenced from other parts of the record or from external sources. These can also be used when translating the ISO metadata to standards that include only a bounding extent. It also include a geographicIdentifier, in this case a location keyword from the NASA GCMD.

<gmd:extent>
    <gmd:EX_Extent id="boundingExtent">
        <gmd:geographicElement>
            <gmd:EX_GeographicBoundingBox id="boundingGeographicBoundingBox">
                <gmd:extentTypeCode>
                    <gco:Boolean>true</gco:Boolean>
                </gmd:extentTypeCode>
                <gmd:westBoundLongitude>
                    <gco:Decimal>-178</gco:Decimal>
                </gmd:westBoundLongitude>
                <gmd:eastBoundLongitude>
                    <gco:Decimal>180</gco:Decimal>                    
                </gmd:eastBoundLongitude>
                <gmd:southBoundLatitude>
                    <gco:Decimal>-78</gco:Decimal>
                </gmd:southBoundLatitude>
                <gmd:northBoundLatitude>
                    <gco:Decimal>75</gco:Decimal>
                </gmd:northBoundLatitude>
            </gmd:EX_GeographicBoundingBox>           
        </gmd:geographicElement>
        <gmd:geographicElement>
            <gmd:EX_GeographicDescription>
                <gmd:geographicIdentifier>
                    <gmd:MD_Identifier>
                        <gmd:authority>
                            <gmd:CI_Citation>
                                <gmd:title>
                                    <gco:CharacterString>NASA/GCMD Location Keywords</gco:CharacterString>
                                </gmd:title>
                                <gmd:date>
                                    <gmd:CI_Date>
                                        <gmd:date>
                                            <gco:Date>2009-01-01</gco:Date>
                                        </gmd:date>
                                        <gmd:dateType>
                                            <gmd:CI_DateTypeCode codeList="http://www.isotc211.org/2005/resources/Codelist/gmxCodelists.xml#CI_DateTypeCode" codeListValue="revision">revision</gmd:CI_DateTypeCode>
                                        </gmd:dateType>
                                    </gmd:CI_Date>
                                </gmd:date>
                            </gmd:CI_Citation>
                        </gmd:authority>
                        <gmd:code>
                            <gco:CharacterString>Location > Geographic Region > Global Ocean</gco:CharacterString>
                        </gmd:code>
                    </gmd:MD_Identifier>
                </gmd:geographicIdentifier>
            </gmd:EX_GeographicDescription>
        </gmd:geographicElement>
        <gmd:temporalElement>
            <gmd:EX_TemporalExtent id="boundingTemporalExtent">
                <gmd:extent>
                    <gml:TimePeriod gml:id="someTimeID">
                        <gml:beginPosition>1846</gml:beginPosition>
                        <gml:endPosition indeterminatePosition="now"/>
                    </gml:TimePeriod>                    
                </gmd:extent>
            </gmd:EX_TemporalExtent>
        </gmd:temporalElement>
        <gmd:verticalElement>
            <gmd:EX_VerticalExtent>
              <gmd:minimumValue>
                <gco:Real>10</gco:Real>
              </gmd:minimumValue>
              <gmd:maximumValue>
                <gco:Real>2810</gco:Real>
              </gmd:maximumValue>
              <gmd:verticalCRS gco:nilReason="unknown"/>
            </gmd:EX_VerticalExtent>
          </gmd:verticalElement>
        </gmd:EX_Extent>
    </gmd:EX_Extent>
</gmd:extent>

XML Example - Vertical Extent

<gmd:verticalElement>
 <gmd:EX_VerticalExtent>
  <gmd:minimumValue>
   <gco:Real> 3600 </gco:Real>
  </gmd:minimumValue>
  <gmd:maximumValue>
   <gco:Real> 3100 </gco:Real>
  </gmd:maximumValue>
  <gmd:verticalCRS xlink:href="http://www.epsg-registry.org/export.htm?gml=urn:ogc:def:crs:EPSG::5715" xlink:title="msl depth in meters" xlink:actuate="onRequest"/>
 </gmd:EX_VerticalExtent>
</gmd:verticalElement>

Usage

Where are EX_Extent objects?

Crosswalks

This table reflects the MENDS voting recommendations pertaining to the mapping of ECHO bounding coordinates to ISO.

Revisions

The revision of 19115 adds extents to:

1. CI_ResponsibleParty to describe spatial/temporal extents of responsibilities.
2. MD_Constraints to describe spatial/temporal extents of constraints.

ISO 19115-1 introduces the capability for data providers to document the temporal resolution of the metadata resource using an ISO 8601-compliant string.