Reposition the UK constituency and local-authority hex maps so they follow the UK's shape #1409

Problem

The UK hex maps for constituencies (650, 2024 boundaries) and local authorities (361, April 2023 boundaries) place many hexes poorly. Neighbouring areas aren't next to each other, and parts of the map don't resemble the UK's shape. That makes both maps hard to read in the v3 "Local areas" tab and the v2 constituency and local-authority views.

Where the positions come from today

• Constituencies: x and y in each constituency result. They originate in policyengine-uk-data's constituencies_2024.csv, which .py copies as src/policyengine/data/uk_geography/constituencies_2024.csv.
• Local authorities: x and y in each local-authority result. They come from the simulation API's static_runtime_files/uk_local_authorities/coordinates_lad23.csv, which .py copies as local_authorities_2023.csv. The Public API's own list (Request UK local-area breakdowns, fix the Northern Ireland region name, and update .py to 6.10.0 policyengine-api#4024) now uses the same positions.

What to do

• Pick better layouts for both maps, ideally maintained ones that already cover these boundary sets. For example, Open Innovations publishes HexJSON layouts for UK constituencies and local authorities. Check their licence and that their codes match our 650 constituency and 361 local-authority codes.
• Make the hexes follow the UK's shape (England, Wales, Scotland and Northern Ireland recognisable, and neighbouring areas next to each other where possible), with no two areas sharing a position.
• Do this together with Own the UK constituency hex-map layout in the frontend #1190, which moves the hex layout into the frontend. Once the app owns the layout, it can use the new positions without the Public API or the simulation API changing their results.
• Add a test that every one of the 650 constituency codes and 361 local-authority codes has exactly one position, and that no two share one.

Related

• Own the UK constituency hex-map layout in the frontend #1190: own the UK constituency hex-map layout in the frontend
• UK local-area breakdowns on request, in v2 and v3 #1398: UK local-area breakdowns on request, which is also adding geographic maps as the default view