THE ELECTION in July for the upper house of Japan’s parliament was “remarkably unfair”, Kazuhiko Tomita, a judge on the northerly island of Hokkaido, ruled in October. Worse, it was held in a “state of unconstitutionality”. He was referring to Japan’s severe malapportionment—the division of the country into legislative districts with widely differing populations.

In Miyagi there are almost 976,000 registered voters for every member the prefecture sends to the upper house of the Diet, or parliament. In Fukui prefecture, the equivalent figure is below 326,000. That means, in effect, that voters in Fukui get three times more representation in the upper house than their counterparts in Miyagi. The discrepancies in the lower house are not quite as bad. The most populous district, in Tokyo, has only twice the voters of the least populous, in Tottori, a largely rural prefecture on the west coast.

Japan’s constitution is a little woolly on how districts are to be drawn up. It gives the authority to do so to the Diet itself, but states, “All of the people are equal under the law” and “There shall be no discrimination because of race, creed, sex, social status, family origin, education, property or income.” Campaigning lawyers have repeatedly used these clauses to challenge malapportionment in the courts. Hidetoshi Masunaga leads the group that brought the case decided last month in Hokkaido. As he observes, “One man, 0.5 votes” is not exactly democratic.

The courts have repeatedly ruled against malapportionment, although they typically decline to throw out the results of elections held with skewed maps. Instead, judges have established a principle that the biggest constituency in the lower house should have no more than double the voters of the smallest. The maximum discrepancy in the upper house is 3:1.

The Diet has repeatedly adjusted district boundaries in an attempt to conform to this rule. But lawmakers have been reluctant to abandon the idea that there should be at least one member in both houses from each of Japan’s 47 prefectures.

Apportionment is a problem in many democracies. America’s constitution allots two senators to each state, regardless of population, meaning that Wyoming has a senator for every 290,000 residents, versus one for every 20m Californians. In Malaysia, the biggest district in parliamentary elections last year had eight times the population of the smallest. Moreover, the difference in Japan has narrowed markedly since the courts began to weigh in. The ratio between upper-house districts used to be as much as 6:1, says Taku Sugawara of the University of Tokyo.

But in Japan malapportionment is particularly persistent and severe because of the country’s unusual demography. Big cities such as Tokyo continue to grow, even as the population as a whole shrinks. Some rural prefectures are losing people at an increasing rate.

The disparities in population will again exceed the limits set by the courts by the time the next election comes around, says Kenneth McElwain of the University of Tokyo. Hokkaido’s population is projected to shrink by a third in the next two decades. Three-quarters of its municipalities could disappear in the coming years, according to the Japan Policy Council, a think-tank. It is huge, accounting for 20% of Japan’s territory, but only 4% of its population. Its MPs will end up representing ever larger districts. That will mean less contact with voters, who will already be feeling left behind by demographic change.

Moreover, the rapid shrinking of the rural population means that each new electoral map quickly becomes biased in favour of relatively elderly and conservative districts in the countryside, at the expense of big cities. That benefits the ruling Liberal Democratic Party, which is stronger in rural areas than urban ones. It dominates the Diet, and its MPs have naturally been reluctant to embrace wholesale electoral reform. That, says Mr Masunaga, is why he and his colleagues have turned instead to the courts. The next step, says Noriyuki Okuyama, a lawyer involved in the Hokkaido suit, is to take their case to the Supreme Court. “One person, one vote is a prerequisite for democracy,” he insists. ■

This article appeared in the Asia section of the print edition under the headline "Japan’s electoral map favours the ruling party"