First Look and Analysis: State House and Senate County Groupings

Yesterday the Census Bureau released the population data North Carolina needed to begin the redistricting process for everything from Congressional to town council districts across the state.  

While we may revisit other aspects of redistricting in future analysis, this post will focus on the State House and State Senate districts and, specifically, how the court-mandated Stephenson Criteria will cause North Carolina’s counties to be grouped when state legislators begin redrawing legislative districts this fall. 

Developing a solid grasp of the county “grouping” requirement is the most valuable insight you need to understand North Carolina’s legislative redistricting process.  Two important notes: first, Democrats generally refer to a county “grouping” or “group” as “clustering” or a “cluster” (more on why in a future post). Second, the grouping requirement does not apply to drawing Congressional Districts in North Carolina.

First, some background on what the Stephenson Criteria are and how they became the governing principle in legislative redistricting in North Carolina: 

In 2001, the Democratic majorities in the General Assembly began drawing the State House and State Senate districts intent on maintaining their majorities.  The House and Senate plans went to great lengths to construct districts that favored the party drawing the maps. For example: the 2001 State Senate map – known as N.C. Senate Plan 1C – divided 51 of North Carolina’s 100 counties:

The 2001 State House map – Sutton House Plan 3 – split 68 counties, over two-thirds of the state’s 100 counties.

Dividing counties to form General Assembly districts is a relatively new phenomenon in North Carolina.  Before 1982, state legislators kept counties whole when drawing General Assembly districts because, dating back to the original 1776 version, North Carolina’s Constitution prohibited dividing counties. This requirement is generally known as the “Whole County Provision” and can be found in Article II, Sections 3 and 5:

Section 3: No county shall be divided in the formation of a senate district;”

Section 5: “No county shall be divided in the formation of a representative district;”

After the General Assembly adopted the 2001 State House and Senate redistricting plans that split a majority of the state’s counties, a man named Ashley Stephenson from Washington, North Carolina filed a lawsuit asking state courts to enforce the constitutional provision requiring legislative maps to keep counties whole. 

Stephenson’s litigation ultimately prevailed, and the North Carolina Supreme Court imposed a series of criteria that govern how legislators draw General Assembly districts in North Carolina.  

The most important was a requirement that the General Assembly comply with the North Carolina Constitution’s Whole County Provision when drawing legislative districts. 

Let’s focus on the key pieces of the Stephenson Criteria that dictate how the state’s counties are grouped to form the foundation of State House and Senate district maps:

  1. Determine the perfect population for each legislative district by dividing the state’s total census population by the number of districts.  This decade, the ideal population is 86,995 for a State House district and 208,788 for a State Senate district. 
  2. Each district is allowed a population deviation of +/- 5% from the ideal population.
  3. County groupings are permitted to contain more than one legislative district, so map drawers must determine the allowable population variance for multi-district county groupings.  This chart uses the allowed 5% variance to calculate the permissible population ranges of county groupings with more than one member.

4. When constructing the county groupings, counties that are grouped together must be contiguous and the contiguity cannot be a shared single point.  

  • The Stephenson Criteria use a simple methodology for determining the optimal, highest-scoring map that complies with the state Constitution’s whole county requirement.  The constitutional map is the map containing:
    • The most 1-county groupings
    • If tied on 1-county groupings, the most 2-county groupings
    • If tied on 1 and 2-county groupings, the most 3-county groupings
    • If tied on 1, 2 and 3-county groupings, the most 4-county groupings
    • And so on…..

We have independently verified an algorithm a team of Duke data scientists created to determine the county grouping arrangement that best complies with Stephenson criteria.

One of the quantitative analytics experts our firm works with processed the recently-released census data through the algorithm to determine the new County grouping maps for the State House and State Senate. 

In both the House and Senate redistricting plans, there are portions of the maps where legislators will have choices about how to configure the counties.  Those options are inset in the maps below.  Because the General Assembly’s redistricting committees adopted compactness as one of the criteria for assessing plans, we have chosen to evaluate the most compact district configuration.  It is important to note legislators could opt for a different configuration if they determine it better complies with the totality of their redistricting criteria.  

Interestingly, we project the different options in both the State House and Senate maps to produce virtually the same political outcomes, though if the House and Senate chose the less compact option in both maps for Northeastern North Carolina it would give Republicans a chance to pick up an additional seat.

Below are the optimal grouping options for the General Assembly redistricting plans.  There are more detailed notes in these linked House and Senate charts. The charts include data on the political performance of the county groupings, double-bunkings, the projected number of seats that are likely to favor each party and the number of toss up seats.  We generally consider a district to be competitive if the winning party won less than 55% of the vote.

The bottom line in the State House is these groupings could not have come together much better for Republicans. The Republicans almost certainly will retain a majority in the House and have a very good chance at winning a supermajority.  Democrats’ only realistic pathway to a majority is an extreme gerrymander of the large urban counties like Mecklenburg, Wake and Guilford that shuts out Republicans entirely.  While these counties favor Democrats, Republicans win around 35% of the countywide vote and a fair map should make about one-third of the districts competitive for the GOP.

State House County Groupings

The optimal grouping maps for the State Senate redistricting plan worked out much better for Democrats than the House plan.  Republicans are still favored to maintain a majority in the Senate and have a narrow pathway to a supermajority in a favorable election environment.  But Democrats have opportunities for a majority too, if they can implement a gerrymander that maximizes their advantage in urban counties and slightly improve their performance in suburban districts. 

State Senate County Groupings