Shiningtop asks “How does redistricting work?”
First, a little explanation of the process is in order, I think. Every state has a legislature, and for the most part there are maps dividing the state into as many districts as there are legislators; Virginia has a 100-district map for the House of Delegates, and a 40-district map for the Senate; 100/40 is a common setup, by the way, though there are several variations.
In many cases, Senate maps tended to be based on counties, or even taken directly from them, so that each county elected one Senator regardless of population, but in Reynolds v. Sims in 1964 the Supreme Court ruled that both houses of a state legislature had to be elected from districts based on the population. Districts must also be drawn if the state is populous enough to send more than one person to the House of Representatives, which most are.
New Hampshire is an interesting example for all of this, since the state senate has 24 members and single-member districts, while the house has 400 seats filled from 103 districts. As far as I can tell, each county is split into several districts of unequal proportions, and each district elects between 1 and 13 people. Frankly, I think this system is far more complicated than necessary, and I'm flabbergasted that it passed Constitutional muster. New Hampshire has by far both the largest lower chamber, among the biggest of all legislatures in the world, and the biggest disparity in numbers between upper and lower house in the country.
So that's what districts are. The thing is, since they're based on population, they have to be close to equal on that metric based on the most recent Census data, and the Census is taken every ten years, so states tend to redraw their maps every ten years. The idea is that the state legislature will look at how their population has shifted, and change the lines accordingly. Unfortunately, since every state except Nebraska has a partisan legislature, that usually turns into “how can we elect as many members of our party as possible?” A few states, like California, have nonpartisan redistricting commissions, but for the most part it's controlled by party officials.
After the 2010 elections, in which Republicans gained many seats in both houses of Congress and control of a dozen or so state legislatures, Reince Priebus, the incoming RNC chair, was asked what the most important thing they won was. He answered, without hesitation, that the biggest victory was the state legislatures, in part because of redistricting. In quite a few states, Republicans control both houses of the legislature—even without the governorship, that's a great deal of influence over how the districts are drawn for the next ten years, which itself has an enormous impact on who is sent to the state capital and to Congress.
To me, the craziest part is that state legislatures get to draw their own maps. It's an immense conflict of interest by its very nature, and that's not counting the districts that are designed to provide safe seats for rising stars so they can later spring for Congressional bids. Party faithful deciding how people should be grouped together, aiming for their own benefit rather than the interests of the community and the demographics, is an affront to democracy. The primary aims of redistricting, legally, are drawing districts of equal population that keep to existing county and city lines where possible and focusing on minorities when necessary. However, should a political party be able to make a map that massively favors them while managing to adhere to these for the most part, the courts can't do anything; redistricting in general can be ruled on, but partisan concerns are non-justiciable.
