25 MPs will come from the Vidzeme constituency,14 MPs will be elected from Zemgale constituency, 14 from Latgale constituency, and 12 from Kurzeme constituency. There are 100 seats in Saeima.
Compared to the 12th Saeima elections, the number of MPs elected from Rīga constituency has increased by three, while the number of MPs elected from Vidzeme, Latgale and Kurzeme constituencies each has decreased by one.
According to the Saeima Election Law, the Central Election Commission (CVK) determines the number of seats in Saeima from each constituency in proportion to the number of voters in that constituency four months before election day, according to the data provided by the Population Register. Voters residing abroad are included among voters of the Rīga constituency, giving further electoral weight to the capital.
According to the Citizenship and Migration Affairs Office, as of June 5 there were 1,548,100 eligible voters in Latvia, including 545,452 in Riga constituency, 392,374 in Vidzeme constituency, 209,110 in Latgale constituency, 213,716 in Zemgale constituency, and 187,448 in Kurzeme constituency.
You can read an overview of the election process in English at the CVK website.