The purpose of regional classifications used in statistics is to describe regional variations of various phenomena and regional structure. As most regional classifications, the division of sub-regional units is based on the administrative regional division.
The division of sub-regional units was adopted in 1994 as a basic division of the acts on regional policy (Act on regional development 1135/93). In the new act on regional development and management of structural fund activities (7/2014), the division into sub-regional units is no more mentioned as the basis for subsidy areas, so it no longer has a position as an official regional division. The criteria used for forming sub-regional units have mainly been cooperation between municipalities and employment. The Ministry of Economic Affairs and Employment and Statistics Finland have agreed that the division into sub-regional units can still be used as a statistical regional division and Statistics Finland maintains it at least for the time being.
Municipalities, sub-regional units, regions and the statistical grouping of municipalities are the primary regional classifications used in Finland's statistical system. Other municipality-based regional classifications used in statistics are major regions, Economic development centres and Wellbeing services counties. Types of municipalities include the cost-of-living classification, financial capacity classification, language distribution classification and municipality form classification.
As of the beginning of 2015, sub-regional units ceased to be an official regional division, but it is maintained at Statistics Finland for the time being.