----------------------------Original message---------------------------- The "stratum" keyword data element in the FGDC metadata standard responds to a request for an ability to describe "vertical" aspects of a set of data in words. Examples would include "troposphere", "stratosphere", etc for the atmosphere, and "continental shelf", "continental slope", etc for the seafloor. The term was provided to complement the keywords for themes (subject matter), horizontal space, and time. MADomaratz FGDC Secretariat [log in to unmask]