XY HEATMAP

Use when

• patterns across two ordered dimensions: weekday x week, hour x day, section x month
• dense grids where a scatter would be unreadable

Do not use when

• entity rows with mixed-scale metrics (use CH-TAB-02, column-normalized)
• exact value lookup as the primary job (a plain table wins)
• diverging data around a midpoint (needs a diverging scale entry, planned)

See instead

• rows are entities, not an ordered dimension: CH-TAB-02
• few points: CH-COR-01

Alternatives

• CH-TAB-02 (heatmap table for entity rows)
• CH-TIM-07 (calendar heatmap, planned)

Rules

• single-hue ramp from cell_low to cell_high (primary); never a rainbow
• the value is printed in every cell; color alone never carries the number
• cell text flips to the low color above 55% intensity, deterministically
• both dimensions keep their natural order
• global normalization: one scale for the whole grid

Never do this

• rainbow color scales
• cells without printed values
• sorting an ordered dimension by value
• diverging data on a sequential ramp

QA before delivering

• every cell prints its value
• single-hue ramp
• dimensions in natural order
• title names the pattern
• source line present bottom-left

Data shape

{
  "title": "Thursday is the heaviest delivery day in all four weeks",
  "eyebrow": "DELIVERIES . WEEKS 25-28",
  "source": "Source: sample dataset v1, 2026-07-12",
  "columns": [
    "W25",
    "W26",
    "W27",
    "W28"
  ],
  "rows": [
    {
      "label": "Mon",
      "values": [
        12,
        14,
        11,
        13
      ]
    },
    {
      "label": "Tue",
      "values": [
        18,
        16,
        17,
        19
      ]
    },
    {
      "label": "Wed",
      "values": [
        22,
        25,
        21,
        24
      ]
    },
    {
      "label": "Thu",
      "values": [
        38,
        41,
        44,
        47
      ]
    },
    {
      "label": "Fri",
      "values": [
        16,
        15,
        18,
        17
      ]
    }
  ]
}