Baseline Congressional Districts: A Benchmark for Comparison

Every state has a well-defined baseline set of congressional districts free of explicit intent to gerrymander for partisan advantage. They are an important benchmark against which to evaluate actual or proposed districts for that state.

In a nutshell, baseline maps maximize the compactness and cohesion[1] of congressional districts while keeping district populations roughly equal. More fully, baseline maps optimize neutral traditional districting principles — contiguity, using decennial census data, having roughly equal populations, compactness, and cohesiveness — while ignoring political considerations.[2],[3],[4] Moreover, by optimizing cohesiveness directly, baseline districts also indirectly preserve virtually all communities of interest.

Using purely mathematical approaches[5], you can make maps with districts that are more compact but only if they are less cohesive. District boundaries will not tend to align with county boundaries, so many more counties will be split across districts. More cohesiveness is better, because it means voters share more county and regional interests with others in their districts and neighbors are more likely to share the same representative leading to better representation for citizens and more accountability for representatives.

You can also make maps with districts that are more equal in population, but again only if they are less cohesive. Again, district boundaries will not tend to align with county boundaries. Moreover, when you optimize for equality of district population, the districts necessarily become less compact.

While congressional districts within states have tended to extreme equality — North Carolina’s current 13 districts for 9.5 million people differ by at most one person! — the population of congressional districts varies widely across states. Due to the apportionment process, the median congressional district is nearly 30% bigger than the smallest. By tolerating a little deviation in district populations within a state (less than 5–10%), baseline district maps can maximize compactness and cohesion.

Baseline districts look much more natural to the layperson, and mathematical measures of compactness bear this out. Moreover, the districts are also easy to describe, being largely composed of entire counties instead of long meaningless lists of thousands of tiny precincts.

As a bonus, these districts are easy to design. By exploiting the natural compactness of counties and the fact that there are many more counties than congressional districts in states, anyone with a state map of counties and their populations, paper, pencil, and a spreadsheet program can sketch the essence of these districts. Actually creating the maps is slightly more involved, requiring a GIS (like ArcGIS or QGIS) but is nonetheless straightforward.

Despite being free of explicit partisan intent, baseline congressional districts may not be fair politically though, due to the vagaries of political geography — where different kinds of people live in a state. There may be naturally occurring discriminatory effect due to liberal-conservative urban-rural polarization[6] or the distribution of minorities throughout a state, race and ethnicity being a close proxy for aggregate voting tendencies.

As examples, baseline congressional districts for two of the most gerrymandered states in the country, North Carolina and Maryland, are described below and contrasted with the existing districts.

Baseline Congressional Districts for North Carolina

North Carolina has 13 congressional districts but 100 counties. Baseline districts [http://bit.ly/2yEJeAb] look much more natural than current districts to the layperson [choose the “Map of Congressional Districts” tab here: http://bit.ly/2ybXb5M], and several mathematical measures of compactness confirm this (see Exhibit 1 below). Moreover, these districts are much easier to describe, being largely composed of entire counties instead of long lists of thousands of small precincts (see Exhibit 2 below).

Baseline Congressional Districts for North Carolina

Baseline Congressional Districts for Maryland

Similarly, baseline districts for Maryland [http://bit.ly/2gduFMl] are much simpler than the current serpentine districts [choose the “Map of Congressional Districts” tab here: http://bit.ly/2g1QJG0]. The eight districts look much more natural, formal measures of compactness reflect that (see Exhibit 3 below), and the districts are easier to describe (see Exhibit 4 below).

Summary

Baseline congressional districts are an important benchmark against which to evaluate actual or proposed districts for a state. This will be explored further in a future post as will the method for generating them. (Teaser: It’s a modified geometric technique that uses the populations, shapes, and spatial relationships of counties.) Given the data required to generate baseline districts is standardized by the Census, the process is suitable for automation.

This is the second in a series of articles on redistricting and partisan gerrymandering.

Exhibit 1 — North Carolina Congressional District Comparisons

Exhibit 2: Baseline Congressional Districts for North Carolina

Exhibit 3 — Maryland Congressional District Comparisons

Exhibit 4: Baseline Congressional Districts for Maryland

[1] “Cohesion” is shorthand for the traditional districting principle of respect for political boundaries & topographical features, e.g., regions, counties, cities, towns.

[2] “Voting Rights and Democracy: The Law and Politics of Districting,” Richard K. Scher et al.

[3] “The Traditional and the less Conventional, but never dull, Cast of Redistricting Principles,” Karin Mac Donald, retrieved from http://redistrictinginstitute.org/wp-content/uploads/2011/01/Traditional-Redistricting-Principles-Karin-Mac-Donald.pdf.

[4] “The Realist’s Guide to Redistricting: Avoiding the Legal Pitfalls,” J. Gerald Hebert.

[5] Like the approach described here: http://wapo.st/2kFTzFX.

[6] https://thinkprogress.org/supreme-court-snatches-victory-away-from-the-forces-of-gerrymandering-8a92d35b87db#.fmb1fmt5i