Documenting Spatial and Temporal Extents

The Extent Spiral defines the spatial and temporal extent of the dataset. This information can be displayed on maps, profiles and timelines and used in spatial and temporal searches. Most documentation dialects include this information because it is so important to data discovery.

ISO Dialects

The ISO standard supports the definition of multiple extents for each dataset/service. In order to simplify the process of identifying the bounding extent, it is recommended that the id attribute be set = "boundingExtent" (see ISO Extents).

NASA GCMD Directory Interchange Format

The DIF format assumes that place keywords come from the GCMD Location Keywords.

netCDF

Extent information is included in the Attribute Conventions for Data Discovery and ctCDF files as global attributes:

<attribute name="geospatial_lat_max" value="90.0 " type="double"/>
<attribute name="geospatial_lat_min" value="-90.0 " type="double"/>
<attribute name="geospatial_lat_resolution" value="0.0416 " type="double"/>
<attribute name="geospatial_lat_units" value="degrees_north"/>
<attribute name="geospatial_lon_max" value="360.0 " type="double"/>
<attribute name="geospatial_lon_min" value="0.0 " type="double"/>
<attribute name="geospatial_lon_resolution" value="0.0416 " type="double"/>
<attribute name="geospatial_lon_units" value="degrees_east"/>
<attribute name="geospatial_vertical_max" value="0.0 " type="double"/>
<attribute name="geospatial_vertical_min" value="0.0 " type="double"/>
<attribute name="geospatial_vertical_positive" value="up"/>
<attribute name="geospatial_vertical_units" value="m"/>

Many of the attributes included in this spiral can be calculated from the data using standard netCDF Tools if the file is compliant with the NetCDF Climate and Forecast (CF) Metadata Convention. In ncISO these attributes are given as part of the CFMetadata group:

<group name="CFMetadata">
    <attribute name="geospatial_lon_min" value="-180.0" type="float" />
    <attribute name="geospatial_lat_min" value="-80.0" type="float" />
    <attribute name="geospatial_lon_max" value="179.5" type="float" />
    <attribute name="geospatial_lat_max" value="85.0" type="float" />
    <attribute name="geospatial_lon_units" value="degrees_east" />
    <attribute name="geospatial_lat_units" value="degrees_north" />
    <attribute name="geospatial_lon_resolution" value="0.5" />
    <attribute name="geospatial_lat_resolution" value="0.5" />
    <attribute name="time_coverage_start" value="2010-05-29T22:00:00Z" />
    <attribute name="time_coverage_end" value="2011-05-21T20:00:00Z" />
    <attribute name="time_coverage_units" value="seconds" />
    <attribute name="time_coverage_resolution" value="314669.0" />
    <attribute name="time_coverage_duration" value="P0Y0M356DT22H0M0.000S" />
  </group>

THREDDS

The THREDDS dialect defines spatial ranges using start, size, resolution, and units and includes place keywords with vocabulary names.

<geospatialCoverage zpositive="down">
    <northsouth>
        <start>10</start>
        <size>80</size>
        <resolution>2</resolution>
        <units>degrees_north</units>
    </northsouth>
    <eastwest>
        <start>-130</start>
        <size>260</size>
        <resolution>2</resolution>
        <units>degrees_east</units>
    </eastwest>
    <updown>
        <start>0</start>
        <size>22</size>
        <resolution>0.5</resolution>
        <units>km</units>
    </updown>
    <name vocabulary="GCMD Location Keywords">Arctic Ocean</name>
</geospatialCoverage>

Crosswalks

Concept	Description	Paths
Southernmost Latitude	The southernmost latitude of the bounding rectangle. Note: OGC-SOS offering lists may not include the entire dataset. A gml:id attribute can be used to identify the bounding offering.	OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/gml:boundedBy/gml:Envelope/gml:lowerCorner ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:geographicElement/gmd:EX_GeographicBoundingBox/gmd:southBoundLatitude/gco:Decimal THREDDS /thredds:catalog/thredds:metadata/thredds:geospatialCoverage/thredds:northsouth/thredds:start THREDDS /thredds:catalog/thredds:dataset/thredds:geospatialCoverage/thredds:northsouth/thredds:start netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=geospatial_lat_min]
Northernmost Latitude	The northernmost latitude of the bounding rectangle. Note: OGC-SOS offering lists may not include the entire dataset. A gml:id attribute (e.g. gml:id="network-all") can be used to identify the bounding offering.	OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/gml:boundedBy/gml:Envelope/gml:upperCorner ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:geographicElement/gmd:EX_GeographicBoundingBox/gmd:northBoundLatitude/gco:Decimal netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=geospatial_lat_max]
Westernmost Longitude	The westernmost longitude of the bounding rectangle. Note: OGC-SOS offering lists may not include the entire dataset. A gml:id attribute can be used to identify the bounding offering.	OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/gml:boundedBy/gml:Envelope/gml:lowerCorner ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:geographicElement/gmd:EX_GeographicBoundingBox/gmd:westBoundLongitude/gco:Decimal THREDDS /thredds:catalog/thredds:metadata/thredds:geospatialCoverage/thredds:eastwest/thredds:start THREDDS /thredds:catalog/thredds:dataset/thredds:geospatialCoverage/thredds:eastwest/thredds:start netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=geospatial_lon_min]
Easternmost Longitude	The westernmost longitude of the bounding rectangle. Note: OGC-SOS offering lists may not include the entire dataset. A gml:id attribute can be used to identify the bounding offering.	OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/gml:boundedBy/gml:Envelope/gml:upperCorner ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:geographicElement/gmd:EX_GeographicBoundingBox/gmd:eastBoundLongitude/gco:Decimal netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=geospatial_lon_max]
Start Time	The start of the bounding time period	OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/sos:time/gml:TimePeriod/gml:beginPosition ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:temporalElement/gmd:EX_TemporalExtent/gmd:extent/gml:TimePeriod/gml:beginPosition THREDDS /thredds:catalog/thredds:dataset/thredds:timeCoverage/thredds:start THREDDS /thredds:catalog/thredds:metadata/thredds:timeCoverage/thredds:start netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=time_coverage_start]
End Time	The end of the bounding time period	OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/sos:time/gml:TimePeriod/gml:endPosition ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:temporalElement/gmd:EX_TemporalExtent/gmd:extent/gml:TimePeriod/gml:endPosition THREDDS /thredds:catalog/thredds:dataset/thredds:timeCoverage/thredds:end THREDDS /thredds:catalog/thredds:metadata/thredds:timeCoverage/thredds:end netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=time_coverage_end]
Vertical Minimum	The minimum height of the bounding rectangle	ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:verticalElement/gmd:EX_VerticalExtent/gmd:minimumValue/gco:Real THREDDS /thredds:catalog/thredds:metadata/thredds:geospatialCoverage/thredds:updown/thredds:start THREDDS /thredds:catalog/thredds:dataset/thredds:geospatialCoverage/thredds:updown/thredds:start netCDF /nc:netcdf/nc:attribute[@name=geospatial_vertical_min]
Vertical Maximum	The maximum height of the bounding rectangle	ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:verticalElement/gmd:EX_VerticalExtent/gmd:maximumValue/gco:Real netCDF /nc:netcdf/nc:attribute[@name=geospatial_vertical_max]
Place Keyword	A comma separated list of key words and phrases that give the location of the resource. Note: Some dialects include keywords, but they do not include mechanisms for identifying the type. In those cases it is difficult to unambiguously identify place keywords.	ISO /*/gmd:identificationInfo/*/gmd:descriptiveKeywords/gmd:MD_Keywords[gmd:type/gmd:MD_KeywordTypeCode='place']/gmd:keyword/gco:CharacterString THREDDS /thredds:catalog/thredds:dataset/thredds:geospatialCoverage/thredds:name
Place Keyword Vocabulary	If you are following a guideline for the place words/phrases in your "keywords" attribute, put the name of that guideline here.	ISO /*/gmd:identificationInfo/*/gmd:descriptiveKeywords/gmd:MD_Keywords[gmd:type/gmd:MD_KeywordTypeCode='place']/gmd:thesaurusName/gmd:CI_Citation/gmd:title/gco:CharacterString THREDDS /thredds:catalog/thredds:dataset/thredds:geospatialCoverage/thredds:name/@thredds:vocabulary

xPath Note: The xPaths included in this table use several wildcards. // means any path, so //gmd:CI_ResponsibleParty indicates a gmd:CI_ResponsibleParty anywhere in an XML file. /*/ indicates a single level with several possible elements. This usually indicates one of several concrete realizations of an abstract object. For example /*/gmd:identificationInfo could be gmd:MD_Metadata/gmd:identificationInfo or gmi:MI_Metadata/gmd:identificationInfo and gmd:identificationInfo//*/gmd:descriptiveKeywords could be gmd:identificationInfo/gmd:MD_DataIdentification/gmd:descriptiveKeywords or gmd:identificationInfo/srv:SV_ServiceIdentification/gmd:descriptiveKeywords.