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  2. Global Change Master Directory (GCMD)
  3. Global Change Master Directory (GCMD) Keywords

Global Change Master Directory (GCMD) Keywords

The GCMD Keywords are a hierarchical set of controlled Earth Science vocabularies that help ensure Earth science data and services are described in a consistent and comprehensive manner and allow for the precise searching of collection-level metadata and subsequent retrieval of data and services. Initiated over twenty years ago, the GCMD Keywords are periodically analyzed for relevancy and will continue to be refined and expanded in response to user needs. The sets of GCMD Keywords are as follows.

        • Earth Science
        • Earth Science Services
        • Data Centers
        • Projects
        • Instruments/Sensors
        • Platforms/Sources
        • Locations
        • Horizontal Data Resolution
        • Vertical Data Resolution
        • Temporal Data Resolution
        • URL Content Types
        • Chronostratigraphic Units

The information provided on this page seeks to define how the GCMD Keywords are structured, used and accessed. It also provides information on how users can participate in the further development of the keywords.


Keyword Forum PageGCMD Keyword Community Forum

The GCMD Keyword Community Forum provides keyword users and metadata providers with an area for discussion of topics related to the GCMD Keywords. Participants are invited to use this forum to ask questions, submit keyword requests, discuss trade-offs, and track the status of keyword requests.




More Information About the Keywords

GCMD Keyword Structure

GCMD Keyword Structure

The GCMD Keywords are organized using a multi-level hierarchical structure. This hierarchical structure provides a framework by which concepts can be classified and related. The Earth Science and Science Services keyword sets use the following hierarchical structure:

Category > Topic > Term > Variable > Detailed Variable

Categories and Topics represent disciplines and high level concepts. Terms and Variables define subject areas and parameters. Detailed Variables are uncontrolled values that can be added by users to more specifically describe data.

All other keyword sets use hierarchies designed for a specific concept. For example, "Instruments" uses Short Name > Long Name. Short name and long name define the name of the instrument used to acquire the data.

Earth Science Keywords Structure

The Earth Science Keywords have a six-level keyword structure with the option for a seventh uncontrolled field. Category and Topic levels define how the keywords are organized and the associated Earth science discipline within the hierarchy. The Term and Variables levels define the subject area, measured variables/parameters, and the hierarchical-type relationship for the subject area.

Keyword Level Example
Category Earth Science
Topic Atmosphere
Term Weather Events
Variable Level 1 Subtropical Cyclones
Variable Level 2 Subtropical Depression
Variable Level 2 Subtropical Depression Track
Detailed Variable (Uncontrolled Keyword)
Earth Science Services Keywords Structure

The Earth Science Services Keywords have a four-level keyword structure with the option for a fifth uncontrolled field. Category and Topic levels define how the controlled keywords are organized and the associated Earth Science Services discipline associated with the keyword in the hierarchy. The Term and Variable levels define the subject area, the type of software/service being described, and the hierarchical-type relationship for the subject area.

Keyword Level Example
Service Category Earth Science Services
Service Topic Data Analysis and Visualization
Service Term Geographic Information Systems
Service Variable Web-Based Geographic Information Systems
Detailed Variable (Uncontrolled Keyword)
Data Center Keywords Structure

The Data Center Keywords have a short name and long name that define the data center, organization, or institution responsible for distributing the data.

Keyword Level Example
Short Name LP DAAC
Long Name Land Processes Distributed Active Archive Center
Project Keyword Structure

The Project Keywords have a short name and long name that define the name of the scientific program, field campaign, or project from which the data were collected.

Keyword Level Example
Short Name ESIP
Long Name Earth Science Information Partner
Instrument/Sensors Keyword Structure

The Instrument/Sensor Keywords have a short name and long name that define the name of the instrument used to acquire the data.

Keyword Level Example
Short Name MODIS
Long Name Moderate-Resolution Imaging Spectroradiometer
Platform/Sources Keyword Structure

The Platform/Source Keywords have a short name and long name that define the name of the platform used to acquire the data.

Keyword Level Example
Short Name Aqua
Long Name Earth Observing System, Aqua
Locations Keyword Structure

The Location Keywords have a five-level keyword structure with the option for a sixth uncontrolled field and define the name of a place on Earth, a location within Earth, a vertical location, or a location outside of the Earth.

Keyword Level Example
Location Category Continent
Location Type North America
Location Subregion 1 United States of America
Location Subregion 2 Maryland
Location Subregion 3 Baltimore
Detailed Location (Uncontrolled Keyword)
Horizontal Data Resolution Keyword Structure

The Horizontal Data Resolution Keywords have a range structure and define the horizontal resolution of the data.

Keyword Level Example
Resolution Range 1 km - < 10 km
Vertical Data Resolution Keyword Structure

The Vertical Data Resolution Keywords have a range structure and define the vertical resolution of the data.

Keyword Level Example
Resolution Range 1 km - < 10 km
Temporal Data Resolution Keyword Structure

The Temporal Data Resolution Keywords have a range structure and define the vertical resolution of the data.

Keyword Level Example
Resolution Range 1 minute - < 1 hour
URL Content Types Keyword Structure

The URL Content Type Keywords have a type-subtype structure and define the type of URL being referenced.

Keyword Level Example
Type Get Data
Sub-Type Earthdata Search
Chronostratigraphic Units Types Keyword Structure

The Chronostratigraphic Keywords have a five-level keyword structure and define the geologic time of the data.

Keyword Example
Eon Phanerozoic
Era Cenozoic
Period Neogene
Epoch Miocene
Stage Tortonian
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Community Use of GCMD Keywords

Community Use of GCMD Keywords

NASA’s Earth Observing System Data and Information System (EOSDIS) as well as numerous other U.S. and international agencies, research universities, and scientific institutions use GCMD Keywords as an authoritative vocabulary, taxonomy, or thesaurus to describe Earth science data, services, and visualizations. Many of these organizations also use GCMD Keywords to create ontologies for the Semantic Web, and to search and access Earth science data within online metadata catalogues. A representative list of organizations using GCMD Keywords is shown below.

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GCMD Keyword Governance and Community Guide Document

GCMD Keyword Governance and Community Guide Document

The Global Change Master Directory (GCMD) Keyword Governance and Community Guide Document, Version 1.0, is intended to provide the community with a comprehensive resource that describes the governance structures and process for reviewing proposed changes to the GCMD Keywords. The document includes an overview of the structure of the keywords, requirements and recommendations to consider when requesting keyword changes, and instructions for submitting change requests. The process described in this document will be the basis of all future GCMD Keyword reviews. The community is invited to provide feedback.

GCMD Keyword Process

The Change Process Overview diagram conveys the end to end process of a keyword including initial request, triage, approval, notification, and implementation.

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Additional Information

Contact GCMD User Support for questions, comments, or technical issues regarding the GCMD Keywords.

Subscribe to the GCMD/IDN Interoperability Email List to receive keyword release announcements.

The GCMD Keywords should be cited as:

Global Change Master Directory (GCMD). 2016. GCMD Keywords, Version 8.4. Greenbelt, MD: Global Change Data Center, Science and Exploration Directorate, Goddard Space Flight Center (GSFC) National Aeronautics and Space Administration (NASA). URL (GCMD Keyword Forum Page): https://earthdata.nasa.gov/gcmd-forum

Last Updated: Oct 20, 2016 at 12:00 PM EDT

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