Splitting

When you click on the “Analytics” command in DRA 2020, the “Splitting” section helps you understand the degree to which the districts in your map split counties (and vice versa).

You’ll see three parts.

Metrics

The first part presents two new measures of splitting:

The first measurement answers the question “How much are counties cut up by districts?” The ideal value is 1.0 — i.e., no splitting — and larger values mean more splitting. The second measurement answers the complementary question: “How much are districts cut up by counties?” The ideal value is also 1.0, and larger values also mean more splitting.

Rating

The second part presents the rating:

Using historical data and ideal values, both raw values are normalized to a [0–100] scale where bigger is better and then averaged to create a single rating.¹ The thermometer shows that rating which is further categorized below using a 5-point scale.

These metrics are explained in-depth in Measuring County & District Splitting.²

Notes

The third part provides additional details about splitting:

• The number of expected county splits, given the number of districts
• The number counties that are split & the number of times (the number of county splits)
• The counties that have to be split because they have more people than a district, the number of possible single-county districts, and the actual number
• The counties that don’t have to be split because they have too many people but are nonetheless
• The percentage of the overall state population affected by having their county split across districts, and
• The number of expected county splits, given the number of districts

Note: The number county splits can be more than the number of split counties, if a county is split more than once.

Updated below: 12/31/21

City-District Splitting

For a handful of states — Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, Rhode Island, and Wisconsin — where city (or townships) effectively cover the entire state (like counties) but people feel provide a more meaningful set of municipal boundaries, we added city-district analysis to this section.

It’s analogous to county-district splitting, except cities (or townships) replace counties. This rating doesn’t influence the county-district splitting rating for a map and isn’t maintained as a sixth rating.

Footnotes

1. For more details and context, see Ratings: Deep Dive.
2. These metrics build on the ones introduced by Professor Moon Duchin in Appendix 6 of her report for the Pennsylvania Supreme Court (link).