The spatial or temporal topic of the resource, the spatial applicability
of the resource, or the jurisdiction under which the resource is relevant.
Spatial topic and spatial applicability may be a named place or a location
specified by its geographic coordinates. Temporal topic may be a named
period, date, or date range. A jurisdiction may be a named administrative
entity or a geographic place to which the resource applies. Recommended
best practice is to use a controlled vocabulary such as the Thesaurus of
Geographic Names [TGN]. Where appropriate, named places or time periods
can be used in preference to numeric identifiers such as sets of
coordinates or date ranges.
Used for the dc:coverage metadata parameter in the OPF file
Same as ->addDublinCoreMetadata(DublinCore::COVERAGE, $coverage);