The Japanese government's electoral reform panel will soon begin reviewing the allocation of lower house seats in some of the country's 47 prefectures based on the census released Friday, with an aim to amend vote weight disparities.
Preliminary data of the 2020 census showed that a disparity in the weight of a single vote between the most and least populated single-seat constituencies stands at 2.09 times. The Supreme Court has found levels above 2.0 times constitutionally problematic.
The panel is expected to recommend a total of 10 seats to be shifted to Tokyo and four prefectures from each of 10 other prefectures, based on the so-called Adams method of seat allocation to better reflect the size of population in each prefecture.
Some lawmakers and experts are concerned that the expected allocation change would work to the disadvantage of voters in rural areas as more seats will be given to densely populated constituencies.
The panel will present its proposal to Prime Minister Yoshihide Suga within a year after fully-fledged discussions start based on revised census data due in November. Suga's government may submit to parliament a bill to reflect a proposed allocation review in the election law during the 150-day ordinary session expected to start in January.
The next House of Representatives election to be called by October will be held under the current system.
The census showed that a vote weight disparity between the most populated No. 22 constituency in Tokyo and the least populated No. 2 constituency in the western prefecture of Tottori is 2.09 times.
The envisaged review will give five new seats to Tokyo, two to neighboring Kanagawa Prefecture, and one each to Chiba, Saitama and Aichi, while 10 prefectures -- Miyagi, Fukushima, Niigata, Shiga, Wakayama, Okayama, Hiroshima, Yamaguchi, Ehime and Nagasaki -- will each lose a seat.
In the lower house election, voters cast one ballot to choose a candidate in a single-seat constituency and another to select a party for proportional representation.
The Supreme Court has ruled that the lower house elections in 2009, 2012 and 2014 in which the largest vote value gap exceeded two times were "in a state of unconstitutionality" without invalidating their results.