1. The Gerrymander How to Divide and Conquer your Enemy
A Case Study on Map Use Abuse

2. Gerrymander Origin
Gerrymander, or Gerrymandering, is derived from Gerry + Salamander
Elbridge Gerry was the governor of Massachusetts before becoming Vice President under James Madison.
The misshapen district which was drawn and passed through the Massachusetts legislature in 1812 by the Democratic Republicans.
The district resembles a salamander.
This is a form of redistricting in which electoral districts are manipulated for an electoral advantage for one political party.
This careful shaping of the voting district gave them and advantage over there Federalist party rivals.

3. Gerrymander Origin
Elbridge Gerry, the 5th Vice President of the United States. In office from March 4, 1813, to November 23, 1814, under President James Madison

4. This satirical cartoon depicting a district in Essex County, Massachusetts, as a dragon, was printed in the Boston Gazette, March 26, The electoral districts were drawn by Democratic-Republican members of the Massachusetts legislature to favor their incumbent party candidates. Governor Elbridge Gerry signed the redistricting into law, although reluctantly.

5. Gerrymander Origin
Redistricting by gerrymandering is typically used by those of a political party in power, or the incumbents.
This redistricting will then advantage their own party, or disadvantage the opposing party, or members of a racial, national, linguistic, religious, or class group.
Redistricting can especially favor a particular political party in single-winner electoral systems that elect representatives to represent voting districts.
Such systems, are called first past the post, or winner takes all.
Typically, such voting systems favor few political parties, e.g., our democratic and republican parties.

6. Example of Positive Effects of Gerrymandering
In Arizona, the Hopi native American tribe is surrounded by the historically rival Navaho tribe.
In this case there is good cause to elect different representatives to the two tribes that are geographically interlocked.
Another, more contentious case, is a narrow California congressional district along the coast separate from the inland district.
The two districts have different concerns that do not always overlap.

7. Gerrymandering Techniques
Two gerrymandering techniques, packing and cracking, allow maximizing votes for one party while minimizing votes for the opposition.
Packing concentrates opposition voters in a few districts that are already a majority in that party.
Cracking breaks down regions that will dilute the opposition so that a slight majority for the other party.

8. Gerrymandering Example Diagram
Left: Four districts of even “Red” and “Green” party voters, 8 from each party.
Right: Redrawing the balanced electoral districts in this example creates only one packed district of 14 green voters.
The remaining 18 green voters are cracked across the 3 other districts. The result is a 3-to-1 advantage for the “Red” party.

9. Gerrymandering Effects
The effects of gerrymandering can be detrimental to the democratic process
Gerrymandered districts favor incumbents that are difficult to unseat in elections, thus creating safe seats.
Safe districts with incumbents with less incentive to govern by constituents’ needs
Proportional or descriptive representation is then altered
Meaningful campaigns are also influenced, further demoralizing voters.
In the 2002 election, only four incumbents in the US Congress were defeated, the lowest number in history.
This was in part due to redistricting and gerrymandering by incumbents.

10. Gerrymandering Example: Arizona's 2nd congressional district
The unusual division was not drawn to favor politicians, but to separate the Hopi and the Navajo tribes, due to historic tensions.
Since the Hopi reservation is completely surrounded by the Navajo reservation, and in order to comply with current Arizona redistricting laws, some means of connection was required that avoided including large portions of Navajo land, hence the narrow Colorado River connection.

11. Gerrymandering Example: Texas’s 22nd congressional district
This district was the result of redistricting in 2003, when Texas congress had become republican, the first time since Reconstruction
This mid-decade redistricting resulted in six additional seats in US congress

12. Gerrymandering Example: California’s 38th congressional district
District 38 was produced by California's incumbent gerrymandering, as home to democrat Grace Flores Napolitano, who ran unopposed in 2004

13. Gerrymandering Example: Illinois’s 4th congressional district
The unusual "earmuff" shape connects two Hispanic neighborhoods while remaining contiguous by following Interstate 294.

14. Gerrymandering Example: Texas’s 25th congressional district
U.S. congressional districts covering Travis County (outlined in red) in 2002, left, and 2004, right.
In 2003, Republicans in the Texas legislature redistricted the state, diluting the voting power of the heavily Democratic county by parceling its residents out to more Republican districts.
The district in orange is the infamous "Fajita strip" district 25 (intended as a Democratic district), while the other two districts (10 and 21) are intended to elect Republicans.
District 25 has now been redrawn as a result of the 2006 U.S. Supreme Court decision, and is no longer a "Fajita strip."

15. Gerrymandering Example: Texas’s 25th congressional districtU

16. Gerrymandering Example: Texas’s 25th congressional district
The conservative 51st District was renumbered the 50th District after the 2000 census, and was gerrymandered to include the more conservative community of Clairemont Mesa, and to exclude the relatively liberal areas of La Jolla and Univ. of Calif. at San Diego, which were moved to the more-liberal 53rd District.

17. Remedies Redistricting was only allowed after the ten year census
The United States Supreme Court upheld all of the 2003 Texas redistricting engineered by former House Majority Leader Tom DeLay, except for the "fajita" district, which would have affected racial and ethnic minority groups.
This decision now allows politicians to redraw and gerrymander districts as often as they like to protect their political parties and seats, provided they do not harm racial and ethnic minority groups.

18. Remedies
Some states have taken or considered taking steps to revoke this rule
A separate non-partisan redistricting authority would choose districts in order to prevent abuse.
Some examples are:
Washington State Redistricting Commission
Arizona Independent Redistricting Commission
Rhode Island Reapportionment Commission
New Jersey Redistricting Commission
The city of San Diego also uses such a system according to its municipal charter.

19. Shape Constraints
A GIS remedy is consider the shape of a district as a limiting factor.
One way to define shape is to compare a parcel’s perimeter length to its area.
This is:
This value is dimensionless
The value for a circle is 1
The value for a square is
The value for a rectangle five times longer than its end is
Limiting this number below a certain value would also limit gerrymandering.

20. References
Elbridge Gerry, Wikipedia,
California's 50th congressional district, Wikipedia,
Politics of Texas, Wikipedia,
Salamander, Wikipedia,
Longley, Paul A., Goodchild, Michael F., Maguire, David J., Rhind, David W., Geographic Information Systems and Science, Publisher: Wiley