Q4 Peak, Q2 Trough , The Seasonal Pattern Intensifies Year-Over-YearInner arm = 2021 · Outer arm = 2024 · Bars colored by month Figure 65.1 , Q4 Peak, Q2 Trough

A spiral plot maps time-series data along an Archimedean spiral : a curve defined by r = a + bθ , where r is the radius from center and θ is the angle. Each period (month) occupies an equal angular increment ( 2pi ÷ periodsPerCycle ), and the spiral grows outward with each complete revolution. The perceptual mechanism is angular alignment : because each cycle occupies exactly one revolution, the same period in different cycles appears at the same angle in every arm.

A standard time-series line chart over 48 months shows the trend clearly , but to confirm periodicity, the viewer must mentally fold the line back on itself every 12 months and check whether peaks align. That is a non-trivial cognitive task performed entirely in working memory. The spiral performs that folding physically: the chart is already organized so that the same month in 2021, 2022, 2023, and 2024 occupies the same angular position.

The spiral used here is Archimedean (equidistant spacing between arms), not logarithmic or Fermat's. Equidistant arm spacing means each year's ring has the same radial depth , the same maximum bar height is available for every year. A logarithmic spiral would compress inner years and expand outer years, visually underweighting early data. An equidistant spiral is the honest geometric choice when all cycles contain equally important data.

The spiral simultaneously shows two temporal signals: the within-cycle seasonal pattern (which months peak, which trough) and the across-cycle trend (do bars at the same angle grow larger in each successive arm?). In this dataset, both are visible. The Q4 cluster (Oct, Dec, top-left quadrant) grows taller arm by arm , the seasonal peak intensifies. April bars (right side) also grow but remain the shortest at each arm , the seasonal trough persists.

Paste this into Claude Code to generate a working version of this chart, plus its data file. The result will not be a perfect replica , the goal is that the reader can run the prompt, get a chart of this type, and read its source. Generate a complete, self-contained spiral plot in D3 v7. Two files:

The ideas in this chapter didn't appear from nowhere. Ramon Llull, a 13th-century Catalan philosopher, built rotating concentric paper wheels that combined attributes by spinning the inner disk against the outer. Each rotation produced a new conjunction of categories. His Ars Magna (c. 1305) is the oldest known mechanical combinatorial visualization , and the conceptual ancestor of every spiral plot that wraps a time series around a center to make cycles visible. Ramon Llull, 13th century. AI-generated illustration based on a public domain painting (Wikimedia Commons).

The ideas in this chapter didn't appear from nowhere. Ramon Llull, a 13th-century Catalan philosopher, built rotating concentric paper wheels that combined attributes by spinning the inner disk against the outer. Each rotation produced a new conjunction of categories. His Ars Magna (c. 1305) is the oldest known mechanical combinatorial visualization , and the conceptual ancestor of every spiral plot that wraps a time series around a center to make cycles visible. Ramon Llull, 13th century. AI-generated illustration based on a public domain painting (Wikimedia Commons).