There are a number of headings where keywords are input. Some, like “Topic category” are a mandatory ISO requirement.
Extract from Intergovernmental Committee on Surveying and Mapping (ICSM) Metadata Good Practice Guide https://icsm.gov.au/what-we-do/metadata-working-group/metadata-working-group-documents
“…Keywords are the important ideas and topics that summarise and define what your resource
is about. In most search engines, these are indexed and typically normalised to resemble the
base word in order to capture variations. Keywords are useful in discovering and organising
resources…”
“…However, excessive use of keywords that target minor aspects of a resource should be avoided. Consider providing a limit to the number of keywords used and focus on those of most importance…”
General guidelines
For each parameter or observed property supplied in the dataset:
Apply up to four ‘Research theme keywords, GCMD Science Keywords’. Focus on keywords that are synonyms for the parameter, or what the parameter represents.
Apply up to four ‘Research theme keywords, ANZSRC Fields of Research’. Focus on keywords that identify the discipline that produced the dataset, or the discipline it is most likely to belong to.