spec: add spiral-timeseries specification

[github-actions]

New Specification: spiral-timeseries

Related to #5243

---

specification.md

spiral-timeseries: Spiral Time Series Chart

Description

A time series plotted along a spiral (Archimedean or logarithmic), where each full revolution represents one cycle period (e.g., one year). By wrapping temporal data around a spiral, corresponding periods from different cycles align vertically, making recurring seasonal or periodic patterns immediately visible. This layout provides a compact alternative to long horizontal time series for cyclic data, revealing periodicity and trend simultaneously.

Applications

• Visualizing yearly temperature or weather patterns across multiple years, with seasons aligned vertically
• Showing website traffic with weekly or monthly seasonality to identify recurring peaks
• Displaying retail sales cycles where holiday peaks align vertically across years
• Analyzing biological rhythms such as circadian or seasonal patterns in activity data

Data

• date (datetime) — timestamp for each observation
• value (float) — measurement value at each timestamp
• cycle_period (str) — what defines one full revolution of the spiral (e.g., "year", "week", "month")
• Size: 2–10 full cycles, 100–3000 data points
• Example: Daily average temperatures over 5 years, with each year forming one spiral revolution

Notes

• Each full revolution of the spiral corresponds to one cycle period
• Color or line thickness should encode value magnitude along the spiral
• Radial grid lines mark subdivisions within each cycle (e.g., months within a yearly spiral, days within a weekly spiral)
• Label the start of each cycle on the spiral for orientation
• The spiral should expand outward from center, with the earliest data closest to the center
• An Archimedean spiral (constant spacing between revolutions) is preferred for uniform readability
• Include a color bar or legend when using color mapping for values

---

Next: Add approved label to the issue to merge this PR.

---

🤖 spec-create workflow