Every 10 years, the 435 seats in the U.S. House of Representatives are re-allocated among the states according to updated population counts in the national census in a process called apportionment.

Every state, no matter how small, gets one seat; thereafter, additional seats are assigned according to a formula that guarantees that each congressperson represents a similar number of constituents in each state. That means that larger, fast-growing states like Texas and California are likely to gain seats at the expense of smaller states and states with slower population growth.

Apportionment doesn’t merely affect representation in Congress: it also affects how many electoral votes each state gets in the presidential elections (which is equal to the total size of each state’s congressional delegation, including two senators from each state).

Explore what it takes to change the balance of power in Washington. Adjust the sliders below to see how different patterns of population growth among the states will affect apportionment in 2020:

Maine rust belt scenario ‘Border wall’ scenario ‘Independence Day’ scenario Reset all State 2010-2020 projected growth rate

The Detroit-in-Maine scenario Maine is at a relatively low risk of losing its second congressional seat in the 2020 reapportionment. The state would need to lose about 25% of its population – roughly 333,000 residents – in order to lose its second seat. Such a dramatic and quick population loss is very unlikely, but not unprecedented. From 2000 to 2010, the city of Detroit lost roughly a quarter of its population as major car manufacturers left the city. The ‘border wall’ scenario International migration makes up a significant portion of population growth in more urban states. If all international immigration were brought to a halt, then New York would lose one more congressional district in 2020, and California, instead of gaining a seat, would instead keep its current allocation of 54 seats. Meanwhile, more rural states would gain influence: Alabama would be saved from losing one of its congresspeople, and Montana would gain one seat. The alien invasion disaster scenario In the 1996 movie “Independence Day,” Bill Pullman has been elected president and an alien invasion destroys the cities of New York, Washington, D.C., Los Angeles, Chicago, San Francisco, Philadelphia, Atlanta, Denver, Seattle, Pittsburgh, Phoenix, Detroit and Las Vegas. Houston is also blown up in an unsuccessful nuclear counter-attack. Presuming that the population growth rates of un-attacked states would roughly double in order to accommodate refugee survivors, this is what the nation’s new electoral map might look like for the movie’s sequel. Projected congressional seats by state in 2020 based on 2010-2015 population growth trends SOURCE: U.S. Census Bureau INTERACTIVE: Christian MilNeil | @vigorousnorth

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