NetCDF Conventions

Unidata offers a repository and will maintain WWW links for sets of netCDF conventions, as supported by the global `Conventions' attribute described in the Attribute Conventions section of the netCDF User's Guide. The following sets of conventions are currently available (some are under development):

• CF Conventions (Recommended standard)
• ACDD Conventions (Attribute Convention for Dataset Discovery)
• OceanSITES Data Format(Extension of CF Conventions standard for OceanSITES data)
• NCAR-RAF Conventions for Aircraft Data
• AMBER Trajectory Conventions for molecular dynamics simulations
• ARGO netCDF conventions for data centers
• National Oceanographic Data Center NetCDF Conventions
• CF Discrete Sampling Geometries Conventions (CF conventions for observational and point data)
• Global Temperature-Salinity Profile Program conventions
• Developing Conventions for NetCDF-4
• COARDS Conventions (1995 standard that CF Conventions extends and generalizes)
• GDT Conventions (1999 standard that CF Conventions extends and generalizes)
• CDC Conventions (for gridded data, compatible with but more restrictive than COARDS)
• NUWG Conventions (1992-1995 effort to create some observational data conventions)
• PMEL-EPIC Conventions
• Proposals for coordinate conventions and coordinate conventions postings ( 1992-1998 discussions)
• UGRID Conventions for unstructured (e.g. triangular, hex) grids.
• SGRID Conventions for staggered, structured (e.g. ROMS, WRF) grids

If present in a netCDF file, `Conventions' is a global attribute that is a character array for the name of the conventions followed by the file. Originally, these conventions were named by a string that was interpreted as a directory name relative to the directory /pub/netcdf/Conventions/ on the host ftp.unidata.ucar.edu.

This web page is now the preferred and authoritative location for registering a URI reference to a set of conventions maintained elsewhere. The FTP site will be preserved for compatibility with existing references, but authors of new conventions should submit a request to support-netcdf@unidata.ucar.edu for listing on this page.

It may be convenient for defining institutions and groups to use a hierarchical structure for general conventions and more specialized conventions. For example, if a group named XXX agrees upon a set of conventions for required attributes, attribute names, and netCDF representations for certain discipline-specific data structures, they may describe the agreed-upon conventions in a document associated with the name "XXX", and files that followed these conventions would contain the global attribute

    :Conventions = "XXX" ;

Later, if another group agrees upon some additional conventions for a specific subset of XXX data, for example time series data, the description of the additional conventions might be associated with the name "XXX/Time_series", and files that adhered to these additional conventions would use the global attribute

    :Conventions = "XXX/Time_series" ;

It is possible for a netCDF file to adhere to more than one set of conventions, even when there is no inheritance relationship among the conventions. In this case, the value of the `Conventions' attribute may be a single text string containing a list of the convention names separated by blank space (recommended) or commas (if a convention name contains blanks), for example

    :Conventions = "XXX YYY" ;

Typical conventions web sites will include references to documents in some form agreed upon by the community that supports the conventions and examples of netCDF file structures that follow the conventions.

Unidata will maintain this conventions web page and will also make available disk space and web access for additional conventions documents for communities lacking a server on which to publish their own convention hierarchies.