Select Ordinal mapping if you wish to map from the source table to the target table by column order (ordinal) in addition to mapping by column name.
When you are defining a distribution, it is now possible to map from the source table to the target table by column order (ordinal) in addition to mapping by column name. Check Map by ordinal on the Distribute Tables dialog.
The first target column is mapped by the first source column, if they are compatible, the second target column by the second source column, if compatible, and so on.
This feature is useful when the field names may not match another SQL table definition but are defined in the same order.