A link data file is a standard ASCII text file which, for each applicable network link, contains one record with the following information:
| Field: | Name | Contents: |
| 1 | inode | Number of I-node of link (not explicitly used by GRTOOL) |
| 2 | jnode | Number of J-node of link (not explicitly used by GRTOOL) |
| 3 | xi | X-coordinate of I-node of link |
| 4 | yi | Y-coordinate of I-node of link |
| 5 | xj | X-coordinate of J-node of link |
| 6 | yj | Y-coordinate of J-node of link |
| 7 | width | link width in the same units as used for network coordinates |
| 8 | var1 | First data value for link (  ) |
| 9-... | vark | Second, third, ...data values for link (  ) |
The link records can appear in any order, i.e. sorting of the links is not required.
Optionally the link records can be preceded by a label record of the
form:
inode jnode xi yi xj yi width var1 var2 var3 ...
If present, this record allows to identify the data values 
by the
names var1, var2, var3, ....
Any record in a link data file which starts with the character # is
considered as a comment. Comments may appear anywhere in the file, but they
are simply ignored.
Usually, link data files are generated by macro GRMACRO and are processed by program GRLINK. Even though GRMACRO generates link data files with up to 5 data values only, the format of the link data file itself does not impose an explicit maximum for the number of data values.