Abstract:
Black Electoral Geography and Congressional Districting:
The Effect of the Voting Rights Act on Partisan Gerrymandering
Jowei Chen
University of Michigan jowei@umich.edu http://www.umich.edu/~jowei
November 2014
How does the creation of majority-black districts under the Voting Rights Act affect the partisan gerrymandering of congressional districts? To analyze the partisan consequences of racial gerrymandering, I conduct thousands of computer districting simulations, drawing alternative congressional plans that either include or do not include VRA-protected majorityblack districts. I argue that, depending on the political geography of black voters, the VRA can either enhance or limit Republicans' ability to gerrymander districts for their partisan gain.
When blacks reside near extremely conservative white voters (e.g., Western Alabama), the VRA substantially constrains Republican gerrymandering by creating a safe, black
Democratic seat in areas that could otherwise have been strategically drawn into moderately
Republican districts. In these cases, the VRA thus prevents a Republican legislature from maximizing its control over seats. By contrast, when blacks reside near politically liberal or moderate whites (e.g., Atlanta, Georgia), the creation of a majority-black district often enables extreme Republican gerrymandering; specifically, the VRA allows partisan redistricters to choose from a new set of redistricting configurations that are normally geographically impermissible in the absence of the VRA. In such cases, the VRA has the "perverse effect" of helping to elect more Republican legislators.

Does the creation of majority-minority districts under the Voting Rights Act (VRA) increase the number of Democrats or Republicans elected to Congress? Beginning with Erikson
(1972), Cain (1984), and Lublin (1997), several observational studies have suggested that a
"perverse effect" emerges when racial gerrymandering artificially concentrates liberal, black voters into a single VRA district. This concentration deprives surrounding districts of
Democratic voters, thus allowing Republican candidates to win these surrounding districts more easily (Swain 1993). But Shotts (2001; 2002; 2003) argues that the opposite may occur in
Southern states with Republican-controlled partisan gerrymandering: The VRA forces a
Republican gerrymanderer to draw black, reliably Democratic districts. Republican legislatures in the South would have drawn no such left-wing districts in the absence of the VRA (Shotts
2003). Under this argument, the VRA increases Democratic seats.
Almost all states with majority-black districts protected by the VRA's requirement of
Department of Justice preclearance are also controlled by Republican legislatures. Hence, the question of how racial gerrymandering interacts with partisan Republican gerrymandering is a politically salient one. Do majority-black districts perversely empower the election of more
Republicans to Congress by removing Democratic voters from non-VRA districts? Or is this
"perverse effect" outweighed by racial gerrymandering's creation of black Democratic districts that a Republican gerrymanderer would never have otherwise created?
Answering this question requires evaluation of two counterfactuals: How would
Congressional districts have been drawn in a racially-blind world, in the absence of the VRA's majority-minority mandate? Furthermore, how would a Republican legislature have gerrymandered its Congressional districts in the absence of a majority-minority mandate?

To evaluate the first counterfactual, I perform repeated, random computer simulations of the district-drawing process in states with majority-black VRA districts. These simulated districting plans are first drawn in both a race-blind and partisan-blind manner, without intentionally seeking to create any majority-minority districts. I then evaluate the partisanship of these simulated districts using 2008 precinct-level presidential vote shares, thus allowing a comparison of the partisanship of these non-racially-gerrymandered districting plans to the partisanship of the actual, enacted districting plans.
I then conduct a second set of simulations to isolate the effect of the VRA majorityminority mandates: In each state with a majority-black, VRA-protected district, I conduct simulations in which each black VRA district is held as geographically fixed; all remaining districts are then randomly drawn by the computer. This process simulates how districts would have been drawn under a partisan-neutral process under which VRA districts are nevertheless required. Comparing these simulations to the non-VRA simulation results thus isolates the effect of racial gerrymandering from the effect of partisan gerrymandering.
[FIGURE 1 HERE]
To illustrate how these VRA simulations are conducted, consider Alabama, which has seven congressional districts. One of these districts, AL-7, is a majority-black district protected by the VRA. Hence, I perform districting simulations in which the boundaries of district AL-7 are held geographically fixed. The remainder of Alabama is then randomly divided into the state's six remaining congressional districts, and this random districting is conducted in a partisan-blind manner. The upper half of Figure 1 illustrates some examples of these simulations, with AL-7 held fixed. Next, I perform a second set of simulations in which all of Alabama is randomly divided into seven districts, without protecting AL-7 or attempting to intentionally

create any majority-black districts. The lower half of Figure 1 illustrates examples of these non-
VRA simulations. Comparison of these two sets of simulations allows us to estimate the electoral effects of the majority-minority mandate in Alabama, under a partisan-neutral redistricting process.
But how does a majority-minority mandate affect electoral outcomes when Republicancontrolled gerrymandering can be assumed in Southern states? This question is answered by comparing the most Republican-favorable districting plan produced by the VRA and non-VRA simulation procedures. The random simulation procedure simply produces a range of possible districting plans that can be drawn under a given set of rules, such as the requirements of compact, contiguous, and equally-populated districts. Partisan gerrymandering occurs when a state legislature surveys the range of possible districting plans and selects the one that most effectively achieves partisan goals, such as the maximization of Republican seats. Hence, comparison of the most Republican-favorable districting plan produced under the VRA and non-
VRA simulation procedures allows us to estimate the effect of the VRA in states where
Republican control the redistricting process.
The Districting Simulation Algorithm : I implement a computer simulation algorithm that is designed to draw geographically compact, contiguous, and equally apportioned districts and estimate the number of Republican legislators elected under this simulated districting plan.
This section explains this algorithm by illustrating its implementation in Alabama, without requiring any VRA districts.
As of the November 2008 election, Alabama consisted of 2,211 voting precincts. These precincts are the smallest geographic unit at which election results are publicly announced, so

they are used as the building block for the districting simulations. Hence, a complete districting plan consists of assigning each one of Alabama’s precincts to a single legislative district.
The simulation proceeds as follows. Suppose Alabama is to be divided into seven districts, the current size of the state's Congressional delegation. First, seven precincts are randomly chosen and assigned to be the respective "seeds" for each of the seven eventual districts. At this point, there are 2,204 unassigned precincts. Each of these remaining precincts are then assigned to the same district as the geographically nearest of the nine original "seeds."
At this point, Alabama has been divided into seven geographically contiguous districts.
These districts are quite compact but not guaranteed to be equally apportioned by population.
The computer then calculates the most under-populated district, denoted as district i . The computer then identifies the district bordering district i that contains the largest population. This bordering district is denoted as j . Among the set of precincts within j that border district i , the computer randomly selects one precinct and reassigns it from district j to district i . Hence, all districts remain contiguous and relatively compact but are now slightly less malapportioned. This process is repeated, generally for at least several thousand iterations, until every district is within
2% of the ideal target population of a district.
Once the computer has divided all of Alabama into seven equally-populated districts, the districting simulation is complete. An analogous procedure is used for the simulations requiring a
VRA district, except that district AL-7, Alabama's majority-black VRA district, is held as geographically fixed, with the remainder of Alabama divided into six random districts. After completing these two sets of districting simulations, I aggregate the precinct-level McCain-
Obama vote counts within each simulated district, thus calculating the partisanship of each district. With these McCain-Obama vote shares, I then predict the likelihood that each simulated

district elects a Republican legislator using a logit model. This logit model is estimated using data from all 435 congressional districts, producing a mapping from the district's McCain vote share to its likelihood of electing a Republican legislator during the 2008 and 2010 elections.
[FIGURE 2]
As an illustration, Figure 2 reports the McCain vote shares in each simulated district produced by either the VRA or the non-VRA simulation procedures. A total of 100 districting plans are drawn using each of the two procedures, with districts from non-VRA simulations depicted in blue dots and districts from VRA simulations depicted in red dots. For each plan, the seven districts are aligned along the seven points of the x-axis, based on the districts' geographic distance from the centroid of AL-7. Hence, the simulated districts closer to the center of
Alabama's black population (ie, the centroid of AL-7) appear to the left of this plot.
Comparison of the blue and red dots in Figure 2 reveal how the mandating of Alabama's
VRA district, AL-7, alters the partisan composition of surrounding districts in the simulations.
When the VRA district is not required, voters in AL-7 are normally drawn into a moderately
Republican district with roughly 50-60% McCain vote share, which results in a strong probability of electing a Republican legislator. Surrounding districts, encompassing Birmingham and Montgomery, are also typically drawn into moderately Republican districts as well. In fact,
Figure 2 illustrates that under the non-VRA simulation procedure, all seven simulated districts are likely to have over 50% McCain vote share. Figure 3 then uses these simulated district-level vote shares to estimate the probability of electing a Republican legislator, and under the non-
VRA procedure, Alabama has a strong of producing seven Republican legislators from its seven districts.
[FIGURE 3]

But when the simulations require holding Alabama's VRA district (AL-7) fixed, the partisanship of districts changes. The McCain vote share of AL-7 is 39%, representing an unnatural concentration of Democratic voters that makes nearby surrounding districts significantly more conservative. Hence, as Figure 2 illustrates, the closest surrounding districts in
Alabama are noticeably more conservative under the VRA simulations (depicted in red) than under the non-VRA simulations (depicted in blue). But these surrounding districts were already fairly safe Republican seats, so the pro-Republican effects of the VRA in these surrounding districts are significantly outweighed by the fact the Republican candidate is almost guaranteed to lose AL-7, the VRA district itself. Hence, racial gerrymandering harms Republicans in
Alabama.
The opposite result occurs in Virginia, where the VRA protects a single majority-black district, VA-3, which encompasses parts of Norfolk, Newport News, and inner-city Richmond in
Southeastern Virginia. The southeastern portion of Virginia is more politically moderate than
Alabama. Due to the geographic concentration of black Democratic voters in the Norfolk area, a majority-Democratic district emerges naturally in this area during the simulations, even without gerrymandering of any kind. Although this simulated district is not a naturally majority-black district, it is nevertheless a safe Democratic seat. The VRA, by mandating the creation of a majority-black district in the southeastern portion of Virginia, artificially concentrates
Democratic voters in VA-3 in a more extreme manner than occurs under the non-VRA simulations. This extreme concentration effectively robs surrounding districts of Democratic voters and largely eliminates any chance for Democrats to win any of the southeastern districts outside of VA-3. Hence, in contrast to Alabama, the VRA exhibits the "perverse effect" of harming the election of Democrats in Virginia.

This contrast of the VRA's effect in Alabama and Virginia suggests a generalizeable theory: When African-Americans are residentially concentrated in politically liberal or moderate regions (e.g., Southeastern Virginia), the creation of a VRA majority-black district has the
"perverse effect" of helping to elect more Republican legislators. But when blacks reside in more conservative regions (e.g., Western Alabama), racial gerrymandering harms Republicans by creating a black, safe Democratic seat in areas that would normally be drawn into uniformly
Republican districts. This theory implies that the VRA's partisan effects vary by district, and the
VRA may have asymmetric partisan effects, even within the same state.
To test this theory, I use the VRA and non-VRA simulations to measure the partisan effect of each of the 16 majority-black districts located in states requiring VRA preclearance.
Figure 2 presents comparisons of the VRA and non-VRA simulation results for each of these 16majority-black districts. In states containing multiple majority-black districts, such as Georgia, I analyze each majority-black district in isolation: Hence, I perform one set of simulations in which GA-2 is held geographically fixed, while the remainder of Georgia is randomly drawn into
13 simulated districts; a second set of simulations holds GA-4 as fixed, while the remainder of
Georgia is drawn into 13 random districts; an analogous procedure is used to analyze GA-5 and
GA-13, Georgia's remaining majority-black districts.
[FIGURE 4]
To estimate the effect of the VRA under a partisan-neutral redistricting procedure, I then subtract the average number of simulated Republican legislators elected under the non-VRA simulations from the average number of Republicans elected under the VRA simulations. This estimated effect is depicted along the vertical axis of Figure 4, which plots the effect for each of the 16 majority-black districts in VRA states. In this Figure, higher VRA districts are ones that

caused the election of additional Republican legislators in their respective states, while lower districts caused the election of additional Democrats.
The horizontal axis of Figure 4 represents a measure of the regional partisanship of the area in which the black population of each VRA district resides. Specifically, for each majorityblack district, I first calculated the center of the district's black population. From this center, I then identified the nearest 1.4 million people, the approximate size of two congressional districts.
I calculated the McCain vote share among these nearest 1.4 million people, regardless of their race, using 2008 precinct-level vote returns. This McCain vote share thus represents a measure of the partisanship of the geographic region in which the black population of a VRA district resides.
Substantively, this measure is important because it indicates the partisanship of the hypothetical districts to which the black population would have belonged, had the VRA not required the creation of a geographically contorted racial gerrymander.
Figure 4 reveals a strong relationship between the partisan effect of a VRA district and the partisanship of blacks' residential locations. When blacks reside in heavily Republican areas of Alabama and Louisiana, the VRA's majority-minority mandates help to elect more
Democratic legislators. But when blacks reside in more politically moderate regions, as they do in North Carolina and Virginia, the VRA has an aggregate "perverse effect" of promoting the election of more Republicans.
Figure 4 also illustrates how the VRA can cause asymmetric partisan effects within the same state. Blacks in inner-city Atlanta reside in a solidly Democratic part of the city that would have elected a Democratic legislator even in the absence of the VRA. Hence, the VRA's creation of a supermajority-black district, GA-5, has the simple effect of removing Democratic voters from surrounding, moderate suburban districts, thus producing a net increase in the number of

Republican legislators from Georgia. But in southwestern Georgia, blacks reside in a solidly conservative, rural region of the black belt. In the absence of the VRA, this region would have normally been drawn into a safe Republican seat, surrounded by other safe Republican districts.
But the VRA's mandated drawing of GA-2, a majority-black district, in the southwestern region creates a more moderate district that Democrats can more plausibly win; in fact, the seat is currently held by Sanford Bishop, a Blue Dog Democrat. Hence, within Georgia, the VRA's creation of GA-2 helps the Democrats, while the creation of GA-5 helps the Republicans.
Do the VRA's effects on the partisanship of congressional seats remain even if one assumes gerrymandering in southern states is controlled by Republican gerrymanderers? Figure
3 suggests that racial gerrymandering's partisan effects generally remain the same, even when
Republican gerrrymandering occurs. Under partisan gerrymandering, a Republican legislature would survey the range of possible districting plans and select that one that maximizes the number of Republican legislators elected. Figure 3 illustrates that in most states, a VRA majority-minority mandate restricts the range of choices available to the gerrymanderer.
However, the same disparities generally remain between the most Republican-favorable districting plan produced under the VRA simulations and the most Republican-favorable districting plan produced by the non-VRA simulations.
For example, Figure 3 illustrates that when the VRA requires the creation of majorityblack district VA-3, the simulated districting plans produce a range of 6.1 to 6.3 total Republican legislators in Virginia. But when the VRA district is not required, the simulations produce only a range of 5.6 to 5.9 Republican legislators across the state. An efficient Republican gerrymanderer would therefore select the 6.3-Republican legislator plan if the VRA is enforced and the 5.9-Republican legislator plan if the VRA is not in effect.

[FIGURE 5]
How is it possible that the VRA enables a Republican gerrymanderer to achieve outcomes that cannot be achieved without VRA requirements? It might seem, after all, that a majority-minority mandate should merely restrict the set of options available to a redistricter. But geographically, the VRA changes the set of possible plans that a redistricter might enact. New choices are created because in some cases, the political pressures exerted by the Department of
Justice's enforcement of the VRA appear to compel states to take unusual geographic liberties when drawing majority-black districts. VRA majority-minority districts may violate not only the norms of geographic compactness, but also a strict adherence to geographic contiguity. As
Figure 5 illustrates, Virginia's VRA district, VA-3, is an example of such violations. VA-3 includes portions of Norfolk, Hampton, Newport News, and Richmond. These disjoint, African-
American portions are assigned to the same district, while skipping over Farmington,
Williamsburg, and other populated towns whose inclusion would have made the district geographically contiguous. Although VA-3 is not a geographically contiguous district, the
Department of Justice is apparently willing to overlook such violations, which would likely not be permissible in the drawing of non-VRA districts. Hence, the enforcement of VRA majorityminority mandates empowers partisan gerrymanderers to choose from a geographically different set of districting configurations that would not otherwise be available.

Figure 1: Examples of Simulated Districting Plans in Alabama
Examples of Simulations Requiring VRA District AL-7 Held as Fixed:
(District AL-7 Shaded in Black)
Examples of Simulations with No VRA District Requirement:

Figure 2: Effect of the VRA on Alabama's Congressional Delegation
Results of Alabama Simulations
With and Without VRA District AL−7
Simulations without requiring VRA district
Simulations requiring AL−7 held fixed
Enacted Congressional Districting Plan
Closest to AL−7
Furthest from AL−7
Simulated and Enacted Districts Aligned by Geographic Distance from AL−7
Note: Each blue and red dot in this plot represents a simulated district: The blue dots describe simulations that do not require VRA districts, while the red dots describe simulations that require holding fixed AL-7, Alabama's sole majority-black VRA district. Alabama is apportioned seven congressional seats (post-2012); hence, each simulated districting plan contains seven total districts, which are aligned on this plot from left to right according to their geographic distance from the centroid of AL-7. As the red-colored simulations require holding district AL-7 as fixed, this district is always geographically closest to the centroid of AL-7.

FL−24
FL−20
FL−05
AL−07
LA−02
MS−02
VA−03
SC−06
NC−12
NC−01
MI−14
MI−13
GA−13
GA−05
GA−04
GA−02
Figure 3:
Simulations requiring VRA district held fixed
Simulations without requiring VRA district
27
27
27
7
6
4
11
7
13
13
14
14
14
14
14
14
0 5 10 15
Simulated Number of Republican Legislators
Elected to the State’s Congressional Delegation
Note: Each row in this plot depicts two sets of simulations: The upper, red dots describe simulations that do not require VRA districts, while the lower, blue dots describe simulations that require holding fixed the respective VRA district named in each row. For example: In the bottom row of this plot, the upper red dots represent simulations of dividing Georgia into 14 random districts, none of which are guaranteed to be majority-black. The lower, blue dots represent simulations in which enacted district GA-2, a majority-black district, is held as geographically fixed. The simulation procedure then divides the remainder of the state into 13 random districts, thus creating a plan with 14 total districts. The right margin reports each state's number of total congressional districts.

FL−24
Figure 4
VA−3
NC−12
MI−13
GA−5
GA−4
GA−13
NC−1
FL−5
SC−6
GA−2
MS−2
0.40
AL−7
0.45
0.50
0.55
0.60
McCain vote share among the 1.4 million residents closest to the VRA district’s center of black population
LA−2
0.65

Figure 5:
Virginia Congressional District 3, a Majority-Minority, African-American District
(shaded in red)

Figure 6:
Measuring the Geographic Compactness of Congressional District AL-7

Figure 7:
VRA Districts are the Most Geographically Non-Compact
Geographic Compactness of VRA and Non−VRA Districts
VRA Districts
(Majority−Black)
GA−02
FL−24
GA−05
GA−04
MS−02 MI−13
VA−03
AL−07
GA−13
LA−02
NC−12
SC−06
MI−14
Districts Bordering
a VRA District
AL−03 LA−05
GA−01
VA−09
MI−05
FL−26
GA−12
FL−16
FL−16
MI−03
LA−03
FL−12
GA−09
FL−13
FL−02
SC−04
VA−06
FL−15
GA−09
FL−02
NC−10
AL−05
AL−05
FL−05
All Remaining Districts
(Neither a VRA Nor
Bordering a VRA District)
GA−01
LA−03
FL−02
MI−06
FL−19
MI−05
GA−12
MI−02
VA−09
VA−11
LA−05
LA−04
MI−08
VA−05
MI−07
VA−10
0
(Most Compact)
500000 1000000 1500000
(Least Compact)
Population within the District’s Convex Hull but Excluded from the District