It comprises the municipalities of Amieva, Cabrales, Cabranes, Cangas de Onís, Caravia, Colunga, Llanes, Nava, Onís, Parres, Peñamellera Alta, Peñamellera Baja, Piloña, Ponga, Ribadedeva, Ribadesella and Villaviciosa.

The electoral system uses the D'Hondt method and a closed-list proportional representation, with a minimum threshold of three percent.

Each constituency is entitled to an initial minimum of two seats, with the remaining 39 being distributed in proportion to their populations.

[2][3] Voting is on the basis of universal suffrage, which comprises all nationals over eighteen, registered in Asturias and in full enjoyment of their political rights.

[4][5] Seats are elected using the D'Hondt method and a closed list proportional representation, with a threshold of three percent of valid votes—which includes blank ballots—being applied in each constituency.