Notable Maps
Each state page shows three sets of notable maps, one each for type of plan — congressional, state senate, and state house districts.
There are five notable maps for each type of plan:
- Most proportional
- Most competitive
- Best minority representation
- Most compact, and
- Least splitting
where the five maps correspond to the five Ratings in the Analytics view. Together these maps help you understand the tradeoffs inherent in a state’s political geography.
The maps are drawn from the pool of published maps that are “similar, valid, and realistic.” What we mean by those terms is described below.
“Similar”
Two things make maps similar:
- They are the same type of plan — congressional, state senate, or state house; and
- They have the same official number of districts
Hence, maps that experiment with different numbers of districts won’t be considered as potential Notable Maps.
“Valid”
Notable Maps must also meet the four general requirements for valid maps, i.e., maps must be:
- Complete
- Contiguous
- Free of holes, and have
- ‘Roughly’ equal populations
“Donut hole” districts are districts that are fully embedded within one other district (the donut).
“Realistic”
The goal of Notable Maps is to help people understand the tradeoffs between the five factors for a state’s political geography.
Note: These criteria were updated 5/19/21 to distinguish between the most proportional, most competitive, and best minority representation Notable Maps, on the one hand, and the most compact and least splitting Notable Maps, on the other.
To that end, the most proportional, most competitive, and best minority representation Notable Maps must meet the following criteria:
- Proportionality ≥ 20
- Competitiveness ≥ 10
- Compactness ≥ 20
- Splitting ≥ 20
These filters weed out outlier maps that don’t make realistic tradeoffs, like this one:
This map courtesy of @HydeVoltyge (tweet).
In contrast, the most compact and least splitting Notable Maps do not have to have minimum proportionality, competitiveness, or minority representation ratings.
Exceptions
To accommodate some special circumstances and the unique political geographies of a few states and allow more maps to be considered, we relax these rules sometimes:
- When a state only has two districts, contiguity is not required — The raw shapefiles for AK, HI, ME, NH, and RI all have contiguity issues, and the real-life connectivity in AK and HI is a bear to fix. The contiguity requirement is relaxed for congressional and state legislative maps for these states.
- The “realistic” filters also aren’t applied, when there are only two districts— Drawing congressional maps in the states above as well as in DE, ID, MT, ND, SD, VT, WV, and WY can be challenging.
- State legislative maps, can have embedded districts — This seems to be a somewhat prevalent practice for official state legislative maps (but not congressional ones).
- The minimum splitting rating is also not applied to state legislative maps— The districts tend to be much smaller than congressional ones, so there’s way more unavoidable county-splitting.
- For MA congressional maps, the realistic filters are relaxed — The political geography is such that it’s very difficult to draw proportional congressional districts, so there’s no minimum proportionality and compactness must only be ≥10.
- For WI state legislative maps, contiguity is not required — WI has many “split jurisdictions” — entities comprised of multiple pieces of geography that aren’t all adjacent — that must span the official state legislative districts making them appear to not be contiguous. As with AK and HI above, this would be a bear to fix.
Ratings & Datasets
So that maps are compared on an apples-to-apples basis, the ratings used to compare maps are the ratings maps receive when rated using the default datasets.
Note: If you change the datasets that you use in your map from the defaults, the ratings that you see in the Analytics view can be different than the ratings using the default datasets.
