Electoral regions of Mexico

The electoral regions (circunscripciones electorales) of Mexico are geographic areas composed of various states used for the election of the 200 proportional representation legislators to the Chamber of Deputies.

[1][2] In contrast, the 32 senators-at-large elected to the Senate by the principle of proportional representation are drawn from party lists covering the entire country; the electoral regions therefore play no role in Senate elections.

The regions were initially assigned 20 seats each, but the number was increased to 40 (for a total of 200 plurinominal deputies) for the 1988 election.

Notably, this scheme failed to abide by the criterion of contiguity, with the first region consisting of the Federal District and the non-adjacent states of Puebla and Tlaxcala.

[6][10] In the 1979 to 1985 elections, plurinominal deputies were awarded to those parties that received more than 1.5% of the popular vote but fewer than 60 single-member districts.

[7] Following further reforms in 1986–87, the number of plurinominal seats in the Chamber was increased to its current level of 200 for the 1988 election.

It provided for three possible scenarios: Silvia Gómez Tagle of El Colegio de México described this system as both "inequitable" and "irrational": for example, it was not inconceivable that two parties could each receive over 35% of the popular vote.

Under this scheme, the plurinominal seats were distributed among all the parties in line with their percentages of the popular vote, without taking any account of their first-past-the-post victories.