1. Gerrymandering When Politicians Choose Voters
Alex Tabarrok
Gerrymandering When Politicians Choose Voters

2. Gerrymandering
The Supreme Court has said that (Wesberry v. Sanders 1964) that Congressional districts must be of approximately equal-sized populations.
…"as nearly as practicable one man's vote in a congressional election is to be worth as much as another's.”
Similar ruling for state legislatures in Reynolds v. Sims (1964).
It follows that political districts must often be redrawn to reflect changes in population.

3. Gerrymandering
Gerrymandering is the drawing of political boundaries for partisan or narrowly political purposes.
In 1812 the governor of Massachusetts, Elbridge Gerry, rearranged election districts in order to benefit the republican party. In an editorial cartoon, one of the districts, which was said to look like a salamander, was given a monster's head, arms, and tail and renamed a "gerrymander."
Gerrymandering in the United States has been used both to dilute and strengthen the power of minorities.
There are three main methods of gerrymandering, cracking, packing, and stacking.

4. Cracking
District representation tends to be proportion to minority representation but only if district and minority lines coincide.
Cracking splits districts to dilute one group’s share of the vote.
Figures from George Clark Stealing Our Votes.

5. Packing
Packing puts as many of one group as possible into a super-district. They will win that district but at the price of losing other districts in which they are made the minority.
E.g. take two districts in which group A has 55% of the vote in both districts and make it into two districts in which group A has 90% of the vote in one district and only 25% in the other.

6. Stacking
Stacking, as in stacking the deck, is when district lines are redrawn to make minorities win in as many districts as possible.
Similar to packing but the goal of packing is to concentrate a group to reduce its power while stacking concentrates a group to increase its power.
Stacking often creates “bizarre” looking districts.

7. North Carolina’s 12th Congressional District Circa 1996
At some points runs down a highway. Created to make a voting district with blacks reaching 53.4% of the vote.

8. Gerrymandering as Job Security for Politicians
Gerrymandering is not just about who is represented. Perhaps even more importantly it’s about who gets elected and reelected and reelected.
Gerrymandering is used to create safe districts.
Packing has been supported by a number of prominent minority politicians because even though it may dilute minority vote it makes their seat safe.

9. Gerrymandering can Reduce Seats-Votes Proportionality
In 2012, Democrats won 51 percent of the popular House vote in Pennsylvania but only won 5 out of 18 House seats. A deficit of 4 seats.
Pennsylvania's 7th district.

10. The Complicated Politics of Racial Gerrymandering
Under Section 2 of the Voting Rights Act, states must create districts in which racial minorities have the ability to elect candidates of their choice, so-called “majority-minority districts”.
At least if the minority is sufficiently large and geographically compact for this to be possible and if there is proof of “racially polarized voting,” meaning that whites and minority voters tend to vote for different candidates.
The SC, however, has also ruled, beginning with Shaw v. Reno (1993), that racial districting is a violation of the Equal Protection Clause of the 14th amendment.!
Upshot is that racial reasons cannot be the “predominant factor” in redistricting. 

11. Which District is Unconstitutional?
In Bush. V. Vera the SC said the 30th district unconstitutional because it had been drawn predominantly on the basis of race to elect a black candidate. Justice O’Connor : "[B]izarre shape and noncompactness cause constitutional harm insofar as they convey the message that political identity is, or should be, predominantly racial [C]utting across pre-existing precinct lines and other natural or traditional divisions, is not merely evidentially significant; it is part of the constitutional problem insofar as it disrupts nonracial bases of identity and thus intensifies the emphasis on race.“
Texas District 6, however, did not draw strict scrutiny because it was drawn that way for political rather than racial reasons.
Texas 6th
Texas 30th

13. Partisan Gerrymandering
In January of 2018, a three court panel of Federal judges ruled that a North Carolina redistricting plan was unconstitutional and had been “motivated by invidious partisan intent, so much so that it violated the 14th Amendment’s guarantee of equal protection.
What to do?

14. Alternatives to Gerrymandering: Algorithms
Use an algorithm to maximize “compactness“ while keeping districts of similar-sized population.

15. US Districts by Compactness Algorithm

16. Alternatives to Gerrymandering: Wasted Vote Algorithm
Rather than try to smooth districts by geography an alternative approach tries to eliminate the partisan incentive to gerrymander.
Suppose we have the situation at right. Republicans and Democrats have equal number of voters but Republicans win 3 out of 4 seats due to packing and stacking.

17. Alternatives to Gerrymandering: Wasted Vote Algorithm
Note that in this scenario 4 out of 6 (66%) Democrat votes have been wasted but no Republican votes (0%) have been wasted.
Efficiency Gap=66%-0%=66%
Some votes will always be “wasted” but it is possible to draw boundaries to keep the waste symmetrical, i.e. no partisan bias.

18. Alternatives to Gerrymandering: Cumulative Voting
Create large, multi-member districts, and using a different voting system such as cumulative voting.
Cumulative voting e.g. – a state has 5 representatives. Each voter gets 5 votes which they can allocate in any way that they want. 1 vote each to 5 candidates. 5 votes to 1 candidate etc.
Cumulative voting allows for self-defined minorities.