Global Change Master Directory (GCMD) Keywords are a hierarchical set of controlled Earth Science vocabularies that help ensure Earth science data, services, and variables are described in a consistent and comprehensive manner and allow for the precise searching of metadata and subsequent retrieval of data, services, and variables. Initiated over twenty years ago, GCMD Keywords are periodically analyzed for relevancy and will continue to be refined and expanded in response to user needs. The categories of GCMD Keywords are as follows: (1) Earth Science; (2) Earth Science Services; (3) Data Centers/Service Providers; (4) Projects; (5) Instruments/Sensors; (6) Platforms/Sources; (7) Locations; (8) Horizontal Data Resolution; (9) Vertical Data Resolution; (10)Temporal Data Resolution; (11) URL Content Types; (12) Chronostratigraphic Units.
