Mapping Entity Fields
Mapping streamlines data entry when you create new records that are associated with another record. When two entities have an entity relationship, it is possible to create new related entity records from the associated view visible on the primary entity. When the user creates a new record from an associated view, mapped data from the primary entity record is copied to the form for the new related entity record. You control what data is copied by adding new mappings in the relationship between the two entities. If a record is created any way other than from the associated view of the primary entity, data is not mapped.
Mapping only applies just before a new record is created from an associated view. Users are able to make changes before saving the record. Later changes to the data in the primary record are not applied to the related record.
If the field is an option set (picklist), make sure that the option values are identical between the two option sets. When values are added to an option set, the values are assigned an integer based on the order in which they are added. If they were not added in the same order, the labels for the option values on the target field can be edited so they represent a valid mapping as long as this does not affect existing data. If you later modify either option set, you must also remember to modify the other option set to keep them synchronized. Any invalid option set mappings will cause the target field to use the default option set value.
Generate mappings automatically
It is possible to automatically create mappings for the relationship but this usually is not recommended. This process will map any mappable fields based only on the data type and name of the field. All existing mappings are removed.