A grid data file is a standard ASCII text file which contains for each applicable grid cell one record with the following information:
| Field: | Name | Contents: |
| 1 | xg | X-coordinate of lower left corner of grid cell |
| 2 | yg | Y-coordinate of lower left corner of grid cell |
| 3 | var1 | First data value for grid cell |
| 4-... | vark | Second, third, ...data values for grid cell |
The grid records can appear in any order, i.e. sorting of the grid cell records is not required.
Optionally the grid records can be preceded by a label record of the
form:
xg=distx yg=disty var1 var2 var3 ...
If present, this record allows to identify the data values 
by the
names var1, var2, var3, ....
Any record in a grid data file which starts with the character # is
considered as a comment. Comments may appear anywhere in the file, but they
are simply ignored.
Grid data files are usually generated by program GRLINK and are read by program GRANNOT in order to generate grid displays in to the form of annotation file.