The Ten Four-Seat Provinces: Hotly Contested, Rarely Decisive

Ten constituencies elect four deputies each on 29N, from Álava to Salamanca. They are the tightest on the map: in five of them the PP and the PSOE tied at two seats each in 2023, and in the forecast their allocation differs from the central scenario in between 9% and 78% of simulations. But their 40 seats explain only 14% of the variability of the PP–Vox bloc, and their allocation decides the absolute majority in 3% of simulations. The majority is fought over in the six large provinces. The four-seaters decide something else: how many seats the two-party system loses to Vox.

31 October 2026 · Miguel · Leer en español

Which ones they are and why they matter

With the 2026 seat distribution, which gives 38 to Madrid and 8 to Cádiz, ten constituencies elect four deputies: Álava, Albacete, Burgos, Cáceres, León, Lleida, La Rioja, Lugo, Ourense and Salamanca. Together with the three-seat and five-seat constituencies, they are the largest group, and they add up to 40 of the 350 seats.

They have a particular arithmetic. With four seats and the D’Hondt method, the top party needs more than double the votes of the runner-up to win three, and a third party needs around 15% to get in. The usual result is two and two between the big parties, or three and one if one of them sweeps; with Vox above 15%, the most frequent split becomes two, one and one. Each seat changes hands with a few thousand votes.

The tightest on the map

In 2023, five of the ten ended in a two-two tie between the PP and the PSOE, three in PP 3 and PSOE 1, and Álava and Lleida split among four parties. For 29N, the central scenario draws them differently: PP 2, PSOE 1 and Vox 1 in six of them, PP 3 and PSOE 1 in Ourense, PP 2, PSOE 1 and BNG 1 in Lugo, and one seat per party in Álava and Lleida.

• The most open are Lleida (the allocation changes in 78% of simulations, with four parties each at one seat and a median gap of 3,300 votes), Lugo (72%, where the BNG and the PSOE compete with the PP for the fourth seat) and Álava (53%, four parties at one each).
• The most settled are Salamanca (the central scenario holds in 91%) and Albacete (84%): the PP has two secured and Vox the third.
• Cáceres and La Rioja best show what is at stake: the PP and Vox together win three of four in 53% and 71% of simulations, and the last seat is contested by the three parties with median gaps of 9,000 and 7,400 votes.

It is a historically unstable group. Since 2008, the allocation has changed from one election to the next in four or five of the six occasions in almost all of them; in Salamanca, in all six.

But they don’t decide the majority

Being tight does not mean being decisive. To measure this we grouped the 52 constituencies by size and calculated, across the 50,000 simulations, two things: how much of the variability of the PP and Vox total is due to each group, and how often that group’s allocation is what decides whether the bloc reaches 176 or not.

• The ten four-seaters contribute 14% of the variability of PP + Vox, and their allocation decides the majority in 3.2% of simulations. In the rest, the majority is decided regardless of what happens in them.
• The six large ones (Madrid, Barcelona, Valencia, Sevilla, Alicante and Málaga, with 121 seats) contribute 30% of the variability and decide the majority in 3.7% of simulations. Those with 7 to 10 seats contribute another 24%.
• The three-seaters (24 seats) contribute 6%, and those with one and two seats, 2%.

Seen this way, the phrase “elections are decided in the small provinces” is half true. It is true that each seat there costs fewer votes and changes hands more often. It is not true that they decide the majority: with the PP–Vox bloc at a median of 197 seats, the absolute majority is decided in 94% of simulations without depending on any particular province, and when it does depend on one, it is more likely to be Madrid or Barcelona, because of their size, than Lleida or Lugo.

What they do decide

The four-seaters decide something else, less visible and more interesting: the split within each bloc. In 2023 they gave 20 seats to the PP, 16 to the PSOE, none to Vox and 4 to regional parties. In today’s central scenario they give 19 to the PP, 10 to the PSOE, 6 to Vox and 5 to BNG, Bildu, ERC, Junts and PNV. The PSOE loses six seats there, half of the twelve it loses across Spain, and Vox gains six it did not have in 2023.

The reason is the arithmetic above. When Vox passes 15%, the PSOE’s third seat in these provinces, or its second, is the first to fall. For the PSOE, recovering a point in these provinces is worth more seats than in the large ones. For the PP and Vox, the split of the bloc’s three seats between the two is played out there.

How we calculated it

• Forecast. The 50,000 simulations of the October 31 forecast, with the seats of each constituency in each simulation.
• Variability. Variance decomposition of the PP + Vox seat total by group of constituencies: covariance of each group’s subtotal with the total, divided by the variance of the total. The percentages add up to 100.
• Decides the majority. Simulations in which, fixing the group’s allocation at its central scenario, the bloc goes from reaching 176 seats to not reaching them, or the reverse.
• History. Official Congress results (BOE) from 2008 to 2023 in the ten constituencies that elect four deputies in 2026, by party family.
• Code. analisis_cuatro.py, in the altnalysis repository.