Within the national territory, two types of migratory flow are likely to affect changes in the population of a given geographical zone :
- on the one hand, movements from or to foreign countries, which affect both the migration balance in the zone and the national migration balance ;
- on the other hand, movements within the national territory, between the zone in question and other parts of the territory, which affect the migration balance in the zone but not the national migration balance.
The annual domestic migration rate of a given geographical zone corresponds to the population variation rate attributable to migratory movements between this zone and other parts of the national territory. It is equal to the difference between people entering and leaving the zone related to domestic movement, proportionally to the average population of the zone.