feat(altair): implement ridgeline-basic

[claude]

Summary

Implements ridgeline-basic for altair.

Parent Issue: #539
Base Branch: plot/ridgeline-basic

Files

• plots/ridgeline-basic/implementations/altair.py

Preview

Preview will be uploaded to GCS staging after this workflow completes.

[github-actions]

⏭️ Plot Tests Skipped

No plot files changed

Compatibility:

Note: Only Python 3.13 is required to pass. Python 3.12 is tested for compatibility.

[claude]

AI Review - Attempt 1/3

Quality Evaluation

Evaluator	Score	Verdict
Claude	89/100	approve

Criteria Checklist

Visual Quality

• VQ-001: X-axis labeled "Temperature (°C)", Y-axis via facet month labels
• VQ-002: Grid subtle, elements distinguishable, clean visual design
• VQ-003: Distributions clearly visible with alpha=0.7, white stroke outline
• VQ-004: No label overlap, month names readable, intentional distribution overlap
• VQ-005: Legend not needed (colors match facet row labels)
• VQ-006: Blue-orange gradient is colorblind safe (avoids red-green)
• [~] VQ-007: Image 4677×3126 (close to 4800×2700 target, aspect ratio slightly different)
• VQ-008: Title "Monthly Temperature Distributions" centered and clear

Code Quality (N/A for KISS-style plot scripts per CLAUDE.md)

• CQ-001-005: N/A - Plot implementations use simple script style without functions/classes/docstrings

Correctness

• CR-001: Data accurately represents monthly temperature distributions with seasonal pattern
• CR-002: Full spec compliance:
  • ✅ Overlapping density distributions (negative spacing=-30)
  • ✅ Semi-transparent fills (alpha=0.7, within 0.6-0.8 spec)
  • ✅ Gradient coloring (blue=cold → orange=warm)
  • ✅ KDE smoothing via transform_density
  • ✅ 12 categories, 150 observations each
• CR-003: N/A for KISS-style scripts

Strengths

1. Excellent ridgeline effect: Faceted area charts with negative spacing create authentic overlapping distributions
2. Semantic color gradient: Blue (cold winter) → Orange (warm summer) matches temperature data semantically
3. Clean Altair idioms: Proper use of transform_density, faceting with row, and encoding types
4. Spec adherence: All requirements met (overlap %, transparency, KDE, gradient coloring)

Minor Issues

1. VQ-007 PARTIAL: Image dimensions 4677×3126 vs target 4800×2700 (height is 60×12=720 base ×3 scale = 2160 expected, but facet adds overhead). Could adjust width/height to match exactly.

AI Feedback for Next Attempt

Consider adjusting properties to width=1600, height=50 to get closer to 4800×2700 target dimensions when scaled.

Verdict: APPROVED

The implementation is high quality with excellent visual output matching the ridgeline plot specification. The semantic color gradient, proper KDE smoothing, and overlapping facets create an authentic ridgeline visualization. Minor dimension variance does not impact usability.