How the Spanish general election works

A general election in Spain usually happens every four years, after the government's term in office expires. Yet, Sunday's election is not usual, as it comes a little over six months since the last general election on April 28, and is the fourth ballot of its kind in the past four years.

After the last vote, acting Spanish president, Pedro Sánchez, ruled out support from Catalonia's pro-independence parties, and failed to reach an agreement with other parties in parliament whose votes or abstentions would allow him to form a minority government. As a result, voters in Spain were called back to the ballot box.

On November 10, over 37 million people are registered to vote in the election. Yet, depositing their ballot at the polling station is just the start of the process, as how those votes translate into parliamentary seats depends on a system of proportional representation based on regional party lists and involving two parliamentary chambers.

Closed lists and proportional representation

Spanish elections use direct universal suffrage, which gives every adult citizen a vote. However, voters do not elect individual candidates who belong to a party or who are standing as independents, as in the UK, but choose a regional party list, on which the candidates have been pre-chosen in a preferential order by the parties running.

Proportional representation means that parties gain seats in the Spanish parliament in proportion to the number of votes they get. The lower house, known as Congress, is where laws are presented and debated before they go to the upper house, or Senate, which can propose amendments and veto some legislation.

Parliament's two houses

The Congress, which is made up of 350 MPs who are elected for a four-year term, is the house with the greater legislative power, and can override the Senate's amendments and vetoes with an absolute majority of votes. In the April election, Sánchez's Socialist Party got 123 seats, below the 176 seats needed for a majority.

As for the Senate, its members also serve for four years, with 208 chosen directly and 56 indirectly appointed by the autonomous communities (like Catalonia). The Senate does not have the same legislative powers as the Congress, but its limited responsibilities include the application of Article 155 of the Spanish Constitution, which allows for the suspension of regional powers - an exceptional device used in October 2017 to sack the Catalan government led by Carles Puigdemont.

How seats are allocated

Seats are allocated in the Congress with each of Spain's 50 provinces getting a minimum two seats, with the cities, Ceuta and Melilla, electing one MP each. The other 248 seats are spread among the provinces in proportion to the size of their populations. The regions of Spain's two biggest cities, Madrid and Barcelona, elect 37 and 32 MPs this year.

For the Senate, each of the 47 mainland provinces gets four seats, while island provinces, such as the Balearic or Canary Islands, get one to three seats, depending on their size. Ceuta and Melilla elect two each. Autonomous communities can also appoint at least one senator each and get an additional senator per each million inhabitants.

In April, Catalonia's four provinces elected a total of 48 MPs to the Congress, with the pro-independence Esquerra Republicana Party (ERC) getting the most seats (15). ERC also won 11 of the 16 senators elected in Catalonia, with the Catalan Socialists (PSC) coming second in both houses, with 12 and 3 seats, respectively.

How the numbers could change

Whether that changes after Sunday remains to be seen, but the polls suggest that among the Catalan parties, nothing much will. A few days ago, El Periódico newspaper printed a summary of recent polls, predicting ERC and PSC will get about the same Congress seats, with the other pro-independence party, JxCat, dropping from 7 to 6.

As for Spain as a whole, on average the polls suggest that Pedro Sánchez's Socialists could gain a similar number of seats, while the conservative People's Party would recover from April's low of 66 seats to as high as 93, with the far-right Vox, which won its first seats in April, vying for third place with left-wing Podemos.

Yet, polls also augur a low turnout, as voters tire of another election, with 43% of Spaniards surveyed saying they think the election is important, compared to 55% before the April ballot. Yet, the only way to find out is to wait until Sunday, when polling stations open at 9am, with the first exit polls expected around 10.30pm.