Optional elements are provided at the discretion of the
data set producer. An example is data element 10.7, Contact
Facsimile Telephone. The producer may provide the telephone number
of a contact's facsimile machine if it wishes to do so; otherwise,
the element is not provided.
If the producer chooses to provide optional information, the producer
shall follow the production rules (rules defining mandatory, mandatory
if applicable, and optional status) for any data elements contained therein.
An Image Map of the FGDC's Content Standard for Digital Geospatial Metadata