Vote Weight by Constituency
Electors per Seat by Constituency
The House of Councillors is the one national chamber whose constituencies are exactly prefectures, so a prefecture headcount divides into a seat count with nothing left over. Every district is shown against the two lines that the argument turns on: the national average, and twice the best-served district — the threshold above which the courts have repeatedly been asked to rule. Tottori with Shimane, and Tokushima with Kochi, are single merged districts and are summed.
Sensitivity to the Denominator
Who counts as the electorate is the argument, so the same seat map is divided by four different populations here rather than one being assumed. Only the first splits a published figure: the register reports five-year age bands, so the two single years 18 and 19 are estimated. The row below it splits nothing, and the gap between the two is the size of that estimate's influence on the headline.
Drift Under a Fixed Map
The constituencies drawn today, applied to every year of the fifty-year prefecture panel. This is a counterfactual before 2019 and is meant as one: it measures how far the population has moved under a map that does not move with it, not what the disparity was at the time, which was governed by whatever seat table was then in force. Registered Japanese residents of all ages, the only register count published on this basis for fifty years.
Constituency Detail
All 45 constituencies on the selected denominator. Counts of residents are official statistics exactly as published; the seat complement is the figure fixed in law. Everything else in the table is calculated from those two and carries its formula.