Centered Advantage: A Geographic Measure of Partisan Fairness in Redistricting

We introduce a measure of partisan advantage in redistricting that takes into account a state's political geography. We define a party's geographic baseline seat‐share as the proportion of the state's inhabitants for which the party would win a district centered around the inhabitant's location of residence. If the geographically ideal district for each voter is the most compact district with this voter at its center, a party's geographic baseline is the share of residents for whom the party wins their ideal district. A party's “Centered Advantage” is then the difference between the seats the party wins, and its geographic baseline number of seats. We compute the Centered Advantage for each legislative and congressional 2024 district map for all 50 states using precinct‐level statewide elections results from 2016 to 2020. We observe that Democrats' geographic baseline increases with district size, and that Democrats are underrepresented in nationwide seat aggregates: the GOP has a Centered Advantage of about twenty‐eight U.S. congressional seats, and over a hundred and fifty state legislative seats.