When you use the automated mapping facility, there are cases where you can reduce or avoid additional manual mapping by creating a version of the file copybook specifically for VT mapping.
To illustrate this, consider the following extract from a COBOL copybook:
09 OM-HEADDATE.
11 OM-HEADDATE-CC PIC XX.
11 OM-HEADDATE-YY PIC XX.
11 OM-HEADDATE-MM PIC XX.
11 OM-HEADDATE-DD PIC XX.
The automated mapping facility will generate four 2-byte columns for this field. If you want to map the field to OM-HEADDATE a single DATE column, you will have to delete the four mapping entries, insert a single 8-byte field, and map it to the appropriate DB2® column. You can eliminate part of this by updating the copybook to a single 8-byte field.