Classify each county by area-weighted Köppen class shares: a county is
predominantly its top class when that class covers at least 50% of its
land and leads the runner-up by at least 5 percentage points; otherwise
it is Mixed (133 of 3,143 counties in the 50 states and DC).
- Add build_county_koppen_metric.py (writes data/metrics/koppen.csv) and
apply_koppen_metric_to_climate_data.py (writes koppenZone plus
koppenPrimaryClass/koppenSecondaryClass for Mixed counties).
- Move shared helpers into scripts/common/ (county loading, Köppen
legend, area-weighted raster shares); fix the 180th-meridian raster
window for Aleutians West.
- Add check_climate_data.py to validate the app CSV.
- Draw Mixed counties in app.js as diagonal stripes of their top two
classes, fixed to the ground and following the map at every zoom, with
a crossfade only when the stripe size changes. Filtering a class also
matches Mixed counties where it is primary or secondary.
- Document the rule, display, and pipeline plan in docs/ and update the
README and data-source notes.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
