Complex sentence: Relative to the rest of Finland, the southern coastal areas have a thin and patchy cover of till evidencing a more prominent role of glacial erosion in the area, whereas Ostrobothnia and parts of Lapland stand out for their thick till cover.
Split into simpler sentences: Relative to the rest of Finland the southern coastal areas have a thin and patchy cover of till evidencing a more prominent role of glacial erosion in the area. On the contrary Ostrobothnia and parts of Lapland stand out for their thick till cover.