The narrowest part of the Gulf of Bothnia is called Kvarken. The distance from coast to coast is about 80 km and between the outermost islands only about 25 km. The Kvarken divides the Botnian Bay in the north from the Bothnian Sea in the south and forms a shallow underwater threshold in the Gulf of Bothnia. The deepest spot in the Kvarken is only about 25 m. On the Finnish side there is a large archipelago with many islands many of them have permanent inhabitants. The coastline and the shores are shallow and as the land rising is about 0,8 mm every year the scenery in the archipelago changes rapidly. The Ostrobothnian mainland is low with small rivers and fertile soil. On the Swedish side the archipelago is smaller and the shores are steeper. Especially in the southern part of Västerbotten and in Örnsköldsvik with the High Coast the archipelago is quite different than in Finland.

The Kvarken Region consists the counties Ostrobothnia, Southern Ostrobothnia and Central Ostrobothnia in Finland and the County of Västerbotten and the municipality of Örnsköldsvik in Sweden.

The Ostrobothnian counties, with 57 municipalities in the Province of Western Finland, have 450.000 inhabitants. More than 100.1000 of these have Swedish as their native language and many of the 3500.00 persons who speak Finnish know also Swedish. In the Swedish part of the cross-border region there is 15 municipalities in Västerbotten with 250.000 inhabitants and the municipality of Örnsköldsvik in the county of Västernorrland with 60.000 inhabitants.

The Kvarken Region is sparsely populated, especially in Västerbotten, where the population is concentrated to the coast and the population in the inland and in the mountain area is very sparse.