A person’s change of residence is defined as a migration flow. However, there are different types of migration. Depending on whether they involve crossing a border, they are called either internal or international migration movements. International Migration includes all changes of residence between foreign countries, thus it is also referred to as external migration. In contrast, all changes of residence within the borders of a country are considered internal migrations. Internal migrations can be further distinguished into changes of residence within any given entity (e.g. countries, federal territories, counties, municipalities) without crossing administrative boundaries.
The 1961 census registered statistical migration flows in Austria for the first time, collecting data on the place of residence five years prior to the census. However, this approach only allowed for a rough approximation of migration flows. In 1996 a statistical system was introduced, which registered migration flows between all Austrian municipalities as well as migrations with foreign countries.
Since 2002 migration statistics have been based on administrative registrations and de-registrations derived from the Central Register of Residence (CRR). This has extended statistical coverage to changes of residence from within a municipality down to the level of localities and census tracts. Still not covered by migration statistics, however, are all changes of residence within the same building. Also, since 2002, migration and population statistics have been working with the same data source and thus offer consistent statistical information. Both statistics cover all persons who have registered a main residence in Austria for at least 90 consecutive days.