How many constituents does your representative represent?

This story is excerpted from MT Lowdown, a weekly newsletter digest of original reports and analysis published every Friday.

As lawmakers meet this winter to draft new legislation and negotiate the next state budget, a quirk of Montana’s Constitution means there’s a notable misalignment in the state’s political math: Every representative has one vote in the Montana House of Representatives, but some represent thousands more voters than their neighbors a few seats down.

The state’s current legislative districts, enacted in 2013, divide the state’s population evenly as they were counted in the 2010 census. Since that census, however, certain parts of Montana have been adding residents at breakneck speed, while others have maintained or even lost populations.

The state constitution stipulates that legislative districts are rebalanced after each decade’s census, but it also establishes a schedule that creates the demographic equivalent of a lame congressional session by giving lawmakers elected on the old map a chance to to express the new drafted by the state’s independent Districting and Allocation Commission.

As that process unfolds in this year’s legislature, data compiled by the State Census and Economic Information Center shows how far the state’s political boundaries have slipped.

In several cases, districts experienced population increases of 50% or more in 2010. That means, for example, that House District 65’s Kelly Kortum, a Democrat who now has about 17,800 voters in northwestern Bozeman, represents almost twice as many people as, say, House District 1 Steve Gunderson, a Republican with about 9,500 people in his district in Libby -Area.

Notably, however, overpopulated districts have elected both Republican and Democratic representatives this year, meaning the misalignment of the aging political map gives neither party an apparent political advantage. South of the District of Kortum, for example, Republican Rep. Jane Gillette represents a crowded House District 64 of about 14,500 people — and Republican lawmakers represent an average of about 10,800 voters this year, compared to 10,900 for Democrats.