What to Feed a gerrymander Control 1421 Mathematics Contest in Modeling February 12, 2007
What to Feed a Gerrymander Control # 1421 Mathematics Contest in Modeling February 12, 2007
abstract Gerrymandering, the practice of dividing political districts into winding and unfair geome- tries, has a deleterious effect on democratic accountability and participation. Incumbent politicians have an incentive to create districts to their advantage(California in 2000, Texas in 2003 )so one proposed remedy for gerrymandering is to adopt an objective, possibly com- puterized, methodology for districting. We present two computationally efficient algorithms for solving the districting problem by modeling it as a Markov decision process rewarding traditional measures of district"goodness": equality of population, continuity, preservation of county lines, and compactness of shape. Our Multi-Seeded Growth Model simulates the creation of a fixed number of districts for an arbitrary geography by "planting seeds"for districts and specifying particular growth rules. The result of this process is refined im mensely in our Partition Optimization Model which uses stochastic domain hill-climbing to make small changes in district lines that improve goodness. We include, as an extension,an optimization to minimize projected inequality in district populations between redistrictings As a case study, we implement our models to create an unbiased, geographically simple dis- tricting of New York using tract-level data from the 2000 Census. We conclude with an open letter to members of the New York State Assembly
Abstract Gerrymandering, the practice of dividing political districts into winding and unfair geometries, has a deleterious effect on democratic accountability and participation. Incumbent politicians have an incentive to create districts to their advantage (California in 2000, Texas in 2003) so one proposed remedy for gerrymandering is to adopt an objective, possibly computerized, methodology for districting. We present two computationally efficient algorithms for solving the districting problem by modeling it as a Markov decision process rewarding traditional measures of district “goodness”: equality of population, continuity, preservation of county lines, and compactness of shape. Our Multi-Seeded Growth Model simulates the creation of a fixed number of districts for an arbitrary geography by “planting seeds” for districts and specifying particular growth rules. The result of this process is refined immensely in our Partition Optimization Model which uses stochastic domain hill-climbing to make small changes in district lines that improve goodness. We include, as an extension, an optimization to minimize projected inequality in district populations between redistrictings. As a case study, we implement our models to create an unbiased, geographically simple districting of New York using tract-level data from the 2000 Census. We conclude with an open letter to members of the New York State Assembly
Control 1421 Page 1 out of 35 What to Feed a gerrymander Team 1421 1 What is gerrymandering Gerrymandering is the division of an area into political districts that give special ad- vantages to one group. Frequently, this involves concentrating "unfavorable"voters in few districts to ensure that "favorable"voters will win in many more districts. In order to squeeze all of the unfavorable voters into a few districts, gerrymandering creates snaky and odd shaped regions. The eponymous label was created when politician Elbridge Gerry pio- eered this technique in early 19 n Century and his opponents claimed the districts resembled salamanders igure 1: The original"Gerry-mander"from the Boston Centinel (1812) 1.1 Basic Terminology Packing- Forcing a disproportionately high concentration of a particular group into one district to lessen their impact in nearby districts Cracking Spreading out members of some group in several districts in order to reduce their impact in each of these districts Forfeit district-a district where group A packs the members of group B so that group B wins this district but loses several surrounding districts which B may have von with a different districting scheme
Control # 1421 Page 1 out of 35 What to Feed a Gerrymander Team 1421 1 What is Gerrymandering? Gerrymandering is the division of an area into political districts that give special advantages to one group. Frequently, this involves concentrating “unfavorable” voters in a few districts to ensure that “favorable” voters will win in many more districts. In order to squeeze all of the unfavorable voters into a few districts, gerrymandering creates snaky and odd shaped regions. The eponymous label was created when politician Elbridge Gerry pioneered this technique in early 19th Century and his opponents claimed the districts resembled salamanders. Figure 1: The original “Gerry-mander” from the Boston Centinel (1812) 1.1 Basic Terminology • Packing - Forcing a disproportionately high concentration of a particular group into one district to lessen their impact in nearby districts. • Cracking - Spreading out members of some group in several districts in order to reduce their impact in each of these districts. • Forfeit district - A district where group A packs the members of group B so that group B wins this district but loses several surrounding districts which B may have won with a different districting scheme
Control 1421 Page 2 out of 35 Wasted Vote-A vote cast by a member of group A in a district where A is already assured victory so voting has no bearing on the result. In general, the group with more wasted votes is made worse off by a districting plan 1.2 Why is it so bad? Politicians today still gerrymander federal and state-level electoral districts and the public outcry is still strongly negative. Before we set out to eliminate this practice we should discuss why gerrymandering is considered problematic First off, gerrymandering reduces electoral competition within districts since cracking packing makes elections uncompetitive. Further, incumbent representatives are in no real danger of losing elections so they do not campaign vigorously which can lead to lower voter turnout. Exacerbating the problem, incumbents' increased advantage means they are less incentivized to govern based on their constituents' interests so democratic accountability and engagement mutually deteriorate Gerrymandering also presents the practical problem that it is difficult to explain to voters why district shapes are so labyrinthine. Some districts connect demographically similar but geographically distant regions using thin filaments such as the district depicted in Figure 2 "Niceness "of district shape almost always takes a back seat to political and racial concerns when districts are being created. Example: In the 2000 California realignment, Democrats and Republicans united to design incumbent -favoring districts which resulted in the reeled- tion of all of the 153 involved legislators in 2004. How can one argue that this is in voters However, it should be noted that gerrymandering can be considered appropriate in specific situations. For instance, the Arizona Legislature gerrymandered a division between the historically hostile Hopi and Navajo tribes even though the Hopi reservation is entirely surrounded by the Navajo reservation Congressional District 4 Figure 2: A present-day gerrymander, the Illinois 4th congressional district (The two "earmuffs"are connected by a narrow band along Highway 294
Control # 1421 Page 2 out of 35 • Wasted Vote - A vote cast by a member of group A in a district where A is already assured victory so voting has no bearing on the result. In general, the group with more wasted votes is made worse off by a districting plan. 1.2 Why is it so bad? Politicians today still gerrymander federal and state-level electoral districts and the public outcry is still strongly negative. Before we set out to eliminate this practice we should discuss why gerrymandering is considered problematic. First off, gerrymandering reduces electoral competition within districts since cracking/- packing makes elections uncompetitive. Further, incumbent representatives are in no real danger of losing elections so they do not campaign vigorously which can lead to lower voter turnout. Exacerbating the problem, incumbents’ increased advantage means they are less incentivized to govern based on their constituents’ interests so democratic accountability and engagement mutually deteriorate. Gerrymandering also presents the practical problem that it is difficult to explain to voters why district shapes are so labyrinthine. Some districts connect demographically similar but geographically distant regions using thin filaments such as the district depicted in Figure 2. “Niceness” of district shape almost always takes a back seat to political and racial concerns when districts are being created. Example: In the 2000 California realignment, Democrats and Republicans united to design incumbent-favoring districts which resulted in the reelection of all of the 153 involved legislators in 2004. How can one argue that this is in voters’ best interests? However, it should be noted that gerrymandering can be considered appropriate in specific situations. For instance, the Arizona Legislature gerrymandered a division between the historically hostile Hopi and Navajo tribes even though the Hopi reservation is entirely surrounded by the Navajo reservation. Figure 2: A present-day gerrymander, the Illinois 4th congressional district. (The two “earmuffs” are connected by a narrow band along Highway 294.)
Control 1421 Page 3 out of 35 1.3 The legality of gerrymandering We should be clear on one point: though gerrymandering is objectionable to many, it is legal around the country. Interestingly, the Voting Rights Act of 1965 which eliminated poll taxes and other discriminatory voting policies may have inadvertently increased the prevalence of gerrymandering. One interpretation of the Act was that it mandated nondiscriminatory election results which led to a strange reversal of vocabulary where creating "ma jority minority"districts was considered beneficial. These gerrymandered districts were packed with minorities which guaranteed minority representation in Congress However, in Shaw v. Reno(1993), and later in Miller v. Johnson(1995), the Supreme Court ruled that racial/ethnic gerrymanders were unconstitutional. Nevertheless, Hunt v Cromatrie approved of a seemingly racial gerrymandering since the motivation was mostly partisan rather than racial. The recent case League of United Latin American Citizens v Perry (June 2006) upheld the position that states are free to redistrict as often as they like o long as these redistrictings follow are not purely racially motivated. 2 Assumptions and Notation 2.1 What can we consider when districting? We have compiled the following list of possible factors one might consider is districting a State. The list is ranked with factors we consider more important or legitimate at the top 1. Population equality between districts (legally mandated) 2. Continuity of districts(legally mandated, excepting islands) 3. Respect for legal boundaries(counties, city limits, townships) 4. Respect for natural geographic boundaries 5. Compactness of district shapes 6. Respect for man-made boundaries(highways, parks, etc. 7. Respect for socio-economic similarity of constituents 8. Similarity to past district boundaries 9. Partisan political concerns 10. Desire to make districts(un)competitive 11. Racial/ethnic concerns 12. Desire to protect (or unseat)incumbent politicians We consider only the top seven factors in our model. Factors 9-12 are all related to political or racial concerns which our model is specifically designed to ignore. The case SC State Conference of Branches v. Riley(1982)ruled that past districts(Factor 8)are legitimate tool for creating new districts but we choose to ignore past districts since they are heay avily biased by Factors 9-12
Control # 1421 Page 3 out of 35 1.3 The legality of gerrymandering We should be clear on one point: though gerrymandering is objectionable to many, it is legal around the country. Interestingly, the Voting Rights Act of 1965 which eliminated poll taxes and other discriminatory voting policies may have inadvertently increased the prevalence of gerrymandering. One interpretation of the Act was that it mandated nondiscriminatory election results which led to a strange reversal of vocabulary where creating “majorityminority” districts was considered beneficial. These gerrymandered districts were packed with minorities which guaranteed minority representation in Congress. However, in Shaw v. Reno (1993), and later in Miller v. Johnson (1995), the Supreme Court ruled that racial/ethnic gerrymanders were unconstitutional. Nevertheless, Hunt v. Cromatrie approved of a seemingly racial gerrymandering since the motivation was mostly partisan rather than racial. The recent case League of United Latin American Citizens v. Perry (June 2006) upheld the position that states are free to redistrict as often as they like so long as these redistrictings follow are not purely racially motivated. 2 Assumptions and Notation 2.1 What can we consider when districting? We have compiled the following list of possible factors one might consider is districting a State. The list is ranked with factors we consider more important or legitimate at the top. 1. Population equality between districts (legally mandated) 2. Continuity of districts (legally mandated, excepting islands) 3. Respect for legal boundaries (counties, city limits, townships) 4. Respect for natural geographic boundaries 5. Compactness of district shapes 6. Respect for man-made boundaries (highways, parks, etc.) 7. Respect for socio-economic similarity of constituents 8. Similarity to past district boundaries 9. Partisan political concerns 10. Desire to make districts (un)competitive 11. Racial/ethnic concerns 12. Desire to protect (or unseat) incumbent politicians We consider only the top seven factors in our model. Factors 9-12 are all related to political or racial concerns which our model is specifically designed to ignore. The case SC State Conference of Branches v. Riley (1982) ruled that past districts (Factor 8) are a legitimate tool for creating new districts but we choose to ignore past districts since they are heavily biased by Factors 9-12