Plan the 119th → 120th boundary transition (8 states)

[DTrim99]

Context

Eight states have enacted new congressional maps that take effect
with the November 2026 elections (120th Congress, Jan 2027–):
TX, MO, NC, OH, CA, UT, FL, TN. Source:
https://en.wikipedia.org/wiki/2025%E2%80%932026_United_States_redistricting

Census Bureau doesn't publish GENZ files for the 120th until ~Q1 2027.
Until then, Dave's Redistricting App (CC-BY GeoJSON) is the most
current authoritative source for each state's enacted map.

Asks

• Decide on a parallel-track shape: ship districts/{XX-NN}-119th.h5
  • districts/{XX-NN}-120th.h5 (recommend; simplest for dashboards to
    pick), or version the entire dataset by Congress.
• Source the eight states' enacted maps from Dave's Redistricting
  (or the state's redistricting body where higher-fidelity polygons
  are needed) and add ingestion to the h5 build script.
• For states unchanged 119th → 120th: carry forward the 119th
  boundary file under the 120th name (zero-cost rename).
• When Census publishes GENZ2026 / TIGER 2026, swap to those as
  canonical and remove the Dave's Redistricting interim source.

Suggested order of operations

1. Land Document the boundary vintage of districts/*.h5 files #1143 (boundary-vintage metadata) first so we can tag the new
   files unambiguously.
2. Source + ingest the eight states in any order; each is independent.
3. Track the remaining (unchanged) states under one umbrella PR — they
   are trivial copies.

Related

• Document the boundary vintage of districts/*.h5 files #1143 — document boundary vintage on the existing h5 files
• Move the canonical congressional-district geojson into this repo #1145 — move the canonical geojson into this repo
• Audit 118th → 119th boundary catch-up (GA, NC, NY, AL, LA) #1146 — 118th → 119th boundary catch-up audit

Coordination

• Dashboards consuming district h5 files: georgia-2026-tax-changes,
  nc-stein-2027-tax-proposals, working-parents-tax-relief-act,
  refundable-credit-conversion, plus any future per-state TY 2027+
  dashboard. Each will need to declare which Congress it's modelling
  and pull the matching h5 set.