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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:

  • Earth Science
  • Earth Science Services
  • Data Centers/Service Providers
  • Projects
  • Instruments/Sensors
  • Platforms/Sources
  • Locations
  • Horizontal Data Resolution
  • Vertical Data Resolution
  • Temporal Data Resolution
  • URL Content Types
  • Granule Data Formats
  • Measurement Names
  • Chronostratigraphic Units

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

GCMD Keyword Forum

The GCMD Keyword Forum, now part of the Earthdata Forum, provides keyword users and metadata providers with an area for discussion of topics related to 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.


 

GCMD Earthdata Forum
Image Caption

A screenshot of the GCMD Keyword Forum showing posts and responses provided by the Earthdata community.

More Information About GCMD Keywords

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 LevelExample
CategoryEarth Science
TopicAtmosphere
TermWeather Events
Variable Level 1Subtropical Cyclones
Variable Level 2Subtropical Depression
Variable Level 3Subtropical 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 LevelExample
Service CategoryEarth Science Services
Service TopicData Analysis and Visualization
Service TermGeographic Information Systems
Service VariableWeb-Based Geographic Information Systems
Detailed Variable(Uncontrolled Keyword)

Data Center/Service Provider Keywords Structure

The Data Center/Service Provider Keywords have a four-level keyword structure and a short name/long name that define the data center, service provider, organization, or institution responsible for distributing the data or developing the service.

Keyword LevelExample
Level 0Government Agencies-U.S. Federal Agencies
Level 1NASA
Level 2-
Level 3-
Short NameLP DAAC
Long NameLand Processes Distributed Active Archive Center

Project Keyword Structure

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

Keyword LevelExample
Short NameESIP
Long NameEarth Science Information Partners

Instrument/Sensor Keyword Structure

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

Keyword LevelExample
CategoryEarth Remote Sensing Instruments
ClassPassive Remote Sensing
TypeSpectrometers/Radiometers
Sub TypeImaging Spectrometers/Radiometers
Short NameMODIS
Long NameModerate-Resolution Imaging Spectroradiometer

Platform/Source Keyword Structure

The Platform/Source Keywords have a three-level keyword structure a short name/long name that define the name of the platform used to acquire the data.

Keyword LevelExample
BasisSpace-based Platforms
CategoryEarth Observation Satellites
Sub Category-
Short NameAqua
Long NameEarth Observing System, Aqua

Location 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 LevelExample
Location CategoryContinent
Location TypeNorth America
Location Subregion 1United States of America
Location Subregion 2Maryland
Location Subregion 3Baltimore
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 LevelExample
Resolution Range1 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 LevelExample
Resolution Range1 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 LevelExample
Resolution Range1 minute - < 1 hour

URL Content Type Keyword Structure

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

Keyword LevelExample
URL Content TypeDistribution URL
TypeGet Data
Sub-TypeEarthdata Search

Granule Data Formats Keyword Structure

The Granule Data Formats Keywords have a one-level keyword structure and represent the format of the data that is distributed by the data center.

Keyword LevelExample
Granule_Data_FormatGRIB

Measurement Names Keyword Structure

The Measurement Names Keywords have a three-level keyword structure and define an observable property, usually geophysical, geo-biophysical, physical, or chemical.

Keyword LevelExample
Context_Mediumatmosphere
Objectair
Quantitypressure_anomaly

Chronostratigraphic Units Types Keyword Structure

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

Keyword LevelExample
EonPhanerozoic
EraCenozoic
PeriodNeogene
EpochMiocene
StageTortonian

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.

The 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 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.

 

Additional Information

Access the GCMD Keywords

Submit a Keyword Request

Keyword Release Announcements

GCMD Keyword Forum

GCMD Keywords Citations

The GCMD Keywords should be cited as:

Global Change Master Directory (GCMD). 2024. GCMD Keywords, Version 20.0, Greenbelt, MD: Earth Science Data and Information System, Earth Science Projects Division, Goddard Space Flight Center, NASA. URL (GCMD Keyword Forum Page): https://forum.earthdata.nasa.gov/app.php/tag/GCMD+Keywords

Unless the content is marked with a use restriction or license, GCMD keywords provided from a NASA led mission are licensed as Creative Commons Zero (CC0). There are no restrictions on the use of these GCMD keywords.

Contact Us

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

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

Tool at a Glance

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