Heatmap Chart

Heatmaps display how a single metric varies across the intersection of two categorical dimensions. Each cell in the grid represents the pair (X, Y) and the cell color encodes the magnitude of the chosen measure.

Data Requirements

Explorer Workflow (Standard Mode)

• Drag fields – Place your primary category (e.g., Order Date) in Rows and the secondary category (e.g., Ship Mode) in Columns. Add the numeric field (e.g., Count of Orders) to Metrics.
• Switch the visual – Open the Chart Quick Selector → Heatmap. Semaphor auto-detects the axes and metric based on the drop zones.
• Tune appearance – In Configuration → Heatmap Colors, pick one of the preset palettes (Green is the default) or switch to Custom to set start/end colors. Use “Color scale position” to move the gradient legend to any side of the chart.

• Format values – Use the global Data Labels panel to toggle numeric labels, select the format (number, currency, percent), and adjust font size. Heatmaps always center the label within the cell for readability.

SQL Workflow (Dev Mode)

When your are working in SQL and python, Semaphor infers field roles by column order. Provide two categorical columns followed by a numeric column.

SELECT
  region,          -- Y-axis
  segment,         -- X-axis
  SUM(sales) AS total_sales
FROM orders
GROUP BY 1, 2
ORDER BY region, segment;

Result grid preview:

| region | segment   | total_sales |
| ------ | --------- | ----------- |
| East   | Consumer  | 1_469       |
| East   | Corporate | 877         |
| East   | Home Ofc. | 502         |
| West   | Consumer  | 1_672       |

Switch the card type to Heatmap. Semaphor automatically uses region for the rows, segment for the columns, and total_sales for the value.

Customization Reference