The Unmap statement disables field value mapping specified by a previous Map … Using statement for subsequently loaded fields.
|a comma separated list of the fields that should no longer be mapped from this point in the script. Using * as field list indicates all fields. The wildcard characters * and ? are allowed in field names. Quoting of field names may be necessary when wildcards are used.
|Disables mapping of field Country.
|Unmap A, B, C;
|Disables mapping of fields A, B and C.
|Unmap * ;
|Disables mapping of all fields.