The variation among the ways in which geospatial data are produced
and distributed, the fact that all geospatial data do not have the same
characteristics, and the issue that all details of data sets that are in
work or are planned may not be decided, caused the need to express the
concept of "mandatory if applicable."
This means that the elements must be provided if the data set exhibits
the characteristic defined by the element (or, for data sets that are
in work or planned, it is known that the data set will exhibit).
An example is compound element 4.2, Vertical Coordinate System Definition,
from Section 4, Spatial Reference Information. The element is
mandatory if applicable. So:
- If a data set has vertical (altitude / elevation or depth)
information, the element is applicable and must be provided.
- If the data set does not have vertical information, the element is not
applicable and is not provided.
An Image Map of the FGDC's Content Standard for Digital Geospatial Metadata