The raw data is on disk in binary direct access format.
The data set is described by a data-descriptor file, which contains:
- Name of the binary data set.
- Mapping between grid coordinates and world coordinates.
- Number of variables, abbreviations for variables.
The data-descriptor file is free format, where each field is blank delimeted. It can be created easily with a text editor.
The format of these files is described in detail in Appendix A. For now, it is sifficient to note that the data descriptor file assigns a one to six character abbreviation for each variable in the file. These abbreviations are used in GrADS expressions.