If every state had NC-style clusters, what would they end up like?

[Sorenroy]

What's an NC cluster?

North Carolina minimizes county splits on state legislative level by having groups of counties in which a given number of seats must be nested. These are typically as small as possible.

The North Carolina constitution forbids division of counties. It does permit multi-member districts and multi-county districts.

In larger counties, VRA requirements likely require single-member districts. Formerly (before 2010) VRA districts were drawn in rural areas. There are very few counties with a majority black population, so these districts tended to snake across the landscape trying to connect areas with a majority black population, perhaps dividing small cities based on where the black population lives.

Over time the rural black population has declined, moving first to Washington, Philadelphia, New York, and other northern cities, and now to cities such as Atlanta, Charlotte, and Raleigh where there are better economic opportunities. The overall increase in the total population has required larger legislative districts. If you have stretched across multiple counties to create a black-majority district, and you have to add population, you may be unable to maintain a black majority. This has particularly happened in southeastern North Carolina. At some point you may be assigning persons to districts based on race.

In rural areas of the northeast where there is a substantial black population, you might not have to draw snakes, because you may be packing. If a county is 50% black, the areas where blacks predominate may be 60% or 70% black. In addition, the Gingles condition that whites vote as bloc to prevent election of the black candidate of choice may no  longer hold. With black turnout as high as or exceeding white turnout in many areas, there might be a relatively small cross-over vote needed.

Through 2010, and the initial 2010 redistricting, the VRA districts were drawn first, and then county clusters were drawn around them. After mid-decade litigation, the snakes were eliminated and pure county clustering was used.

The reason for county clustering is that it minimizes county cutting which violates the NC Constitution. Unlike in Texas, where single-member districts in large counties is considered to be a constitutional manner regulation, it is considered a violation of the NC Constitution. Nevertheless, if you draw a whole number of districts in Wake or Mecklenburg or other large counties you avoid an additional split of a district that crosses a county line.

The NC Supreme Court has also ruled that 2-member districts violate equal protection (this might be under the NC Constitution rather than the US Constitution) because it lets some voters vote for two representatives rather than just one, even if there twice as many of them. You might have previously been able to draw a group of counties that had a population equal to two representatives and elected them at large, this is no longer possible. Instead you are going to split one of the counties.

Generally more clusters means fewer county cuts. If you have a county cluster entitled to three representatives, and you can split it on county lines such that one cluster has two representatives, and the other one, and have eliminated a cut.

If clusters have fewer counties, this will tend to produce more of them. There is a belief in North Carolina that you should draw the one county clusters first, then the two-county clusters, and so on. This might not produce the minimum number of clusters, but will generally do a fairly good job.

However it may force fewer clusters and greater deviation. Whenever you set off one cluster you must also ensure that any remaining contiguous groups of counties can be apportioned a whole number of representatives.

This may increase the deviation and require more county cuts. Imagine that you apportion five representatives to an area entitled to 4.85 representatives. This creates an unreasonable -3.0% deviation. But it also forces the 0.15 representatives to be placed in other districts. And what if that area is entitled to 3.15 representatives. Each district must have a population of exactly 1.0500000 quotas. You may be forcing another cut. If the area was entitled to 3.08 representatives you might have been able to divide it on a county line.

This happened in North Carolina in the mid-2010 redistricting. If you look at the area south of Raleigh you will find such districts where little nibbles of counties were bitten off to get exact populations just as offensive as when doing congressional redistricting.

If I were scoring a North Carolina clustering plan, I would score it based on implied county cuts and lowest standard deviation.

Or better based on Texas, I would only penalize division of smaller counties - less than a quota. Ties would be broken based on lowest standard deviation.

I don't want to clip your post, the whole thing does a great job summarizing the history of how the clusters come about, but the examples you give in the bolded paragraph are actually reasonable in deviation under North Carolina's current rules. As long as population does not deviate by more than ±5% off of the ideal district size, it is allowed. So a cluster entitled to 4.85 representatives getting 5 or a cluster entitled to 3.15 representatives getting 3 is actually within that acceptable range. You could even lose a tenth of an entitled delegate in the first example and it would still be fine.

This does create some interesting potentials for states with large counties and lots of reps. Once you start getting up into the double-digit level for entitled representatives, the population deviations start to overlap. A county or county-cluster that is given 10 delegates might be due anywhere from 9.5 to 10.5 based on its population. A district given 11 delegates is due between 10.45 and 11.55 delegates. That overlap on the upper- and lower-ends makes for some variation that depends on the smaller counties and the clusters they make up. So even though county-clusters are determined first, delegates are not necessarily determined until after the clusters are made because potentially larger counties might be given or need to shed a district to optimize down the line.

In North Carolina, our two largest counties are Mechlenburg and Wake, and both received 13 delegates, and both could've only received 13 delegates because they were only within that range. However, in other states where single counties are more dominant, this might come into play. For example, Cook county, Illinois would be entitled to an ideal of ~48.59 districts, but could actually receive between 47 and 51 of the State House's 118 districts depending on what creates optimal later clusters if they were operating under North Carolina's own standards.