Data mapping is crucial in data migration as it defines the structure and relationships of data fields from the source to the target system. By specifying how data elements correlate, it ensures accuracy and integrity during migration. This reduces the risk of data loss or corruption and enhances the efficiency of the migration process. Proper data mapping can also facilitate regulatory compliance by providing a clear audit trail of how data is transformed and transferred, ultimately leading to a smoother transition and better data management post-migration.