One of Finland's 19 regions is called South Ostrobothnia, and it is one of them. Ostrobothnia, Central Ostrobothnia, Central Finland, Pirkanmaa, and Satakunta are all in the same region as it. If you look at the population of the different parts of Finland, South Ostrobothnia is the ninth largest. Seinajoki is the most important city in the area and the regional centre. It is also the largest.
As a cultural area, South Ostrobothnia is bigger than its current borders. It also includes Ostrobothnia, which is a separate region.