The terms in this document that refer to components of a netCDF file are defined in the NetCDF User's Guide (NUG) [NUG] NUG. Some of those definitions are repeated below for convenience.

auxiliary coordinate variable

Any netCDF variable that contains coordinate data, but is not a coordinate variable (in the sense of that term defined by the NUG and used by this standard - see below). Unlike coordinate variables, there is no relationship between the name of an auxiliary coordinate variable and the name(s) of its dimension(s).

boundary variable

A boundary variable is associated with a variable that contains coordinate data. When a data value provides information about conditions in a cell occupying a region of space/time or some other dimension, the boundary variable provides a description of cell extent.

CDL syntax

The ascii format used to describe the contents of a netCDF file is called CDL (network Common Data form Language). This format represents arrays using the indexing conventions of the C programming language, i.e., index values start at 0, and in multidimensional arrays, when indexing over the elements of the array, it is the last declared dimension that is the fastest varying in terms of file storage order. The netCDF utilities ncdump and ncgen use this format (see chapter 10 of the NUG chapter 10 of the NUG ). All examples in this document use CDL syntax.


A region in one or more dimensions whose boundary can be described by a set of vertices. The term interval is sometimes used for one-dimensional cells.

coordinate variable

We use this term precisely as it is defined in section 2.3.1 of the NUG 2.3.1 of the NUG . It is a one-dimensional variable with the same name as its dimension [e.g., time(time)], and it is defined as a numeric data type with values that are ordered monotonically. Missing values are not allowed in coordinate variables.

grid mapping variable

A variable used as a container for attributes that define a specific grid mapping. The type of the variable is arbitrary since it contains no data.

latitude dimension

A dimension of a netCDF variable that has an associated latitude coordinate variable.

longitude dimension

A dimension of a netCDF variable that has an associated longitude coordinate variable.

multidimensional coordinate variable

An auxiliary coordinate variable that is multidimensional.


Recommendations in this convention are meant to provide advice that may be helpful for reducing common mistakes. In some cases we have recommended rather than required particular attributes in order to maintain backwards compatibility with COARDS. An application must not depend on a dataset's adherence to recommendations.

scalar coordinate variable

A scalar variable that contains coordinate data. Functionally equivalent to either a size one coordinate variable or a size one auxiliary coordinate variable.

spatiotemporal dimension

A dimension of a netCDF variable that is used to identify a location in time and/or space.

time dimension

A dimension of a netCDF variable that has an associated time coordinate variable.

vertical dimension

A dimension of a netCDF variable that has an associated vertical coordinate variable.