FUENTECAMBRÓN, Spain — At 48, Ignacio Sotillos García has the dubious distinction of being the youngest inhabitant of his village in Soria, a province of northern Spain.

He shares a home with his elder brother and parents, who are both in their 80s. Only four other houses remain occupied. Still, his village, Fuentecambrón, is doing better than neighboring Cenegro, which lost its last resident three years ago.

Withering as they may be, provinces like Soria, which has 88,000 inhabitants — half of what it had 60 years ago — will be critical to the outcome of Spain’s national election on Sunday, its third since 2015.

These emptying hinterlands are where Spain’s changing demographic and political landscapes collide, making for an utterly new and volatile dynamic that will determine the country’s future.