Definition of Migration.
A migration is defined as a move from one migration-defining area to another (or a move of some specified minimum distance) that was made during a given migration interval and that involved a change of residence. A migrant is a person who has changed his usual place of residence from one migration-defining area to another (or who moved some specified minimum distance) at least once during the migration interval (United Nations, 1970).
Most statistical offices in the United States “define” migration as a relatively permanent change of residence that crosses jurisdictional boundaries (counties in particular), measured in terms of usual residence at a prior point in time, typically one to five years earlier. Local moves within jurisdictions are referred to as residential mobility (Population Association of America, 1988).
Finland: Persons leaving to work abroad for at least one year or to marry and remain abroad permanently.