Accuracy failures lead at 31 , safety incidents, at 8, may be the most under-reported Figure 71.1 , Accuracy failures lead at 31

A Tally Chart is simultaneously a data collection method and a visual display . The tally mark numeral system , four vertical strokes crossed by a diagonal , groups counts in fives, making totals readable at a glance without arithmetic. Historically made with pen and paper, the form conveys something that no bar chart can: the process of counting . Each mark is a discrete event. The chart does not abstract the data into a continuous scale; it preserves the unit nature of what was counted.

The data is a count of discrete events (reported incidents) across a small number of categories with relatively modest counts (8, 31 per category). A bar chart would be more precise, and a dot plot would be more elegant. But the tally form makes an argument that precision does not: these are individually countable events , not a measured quantity. Every mark is an incident that was filed by a real person.

A histogram bins continuous values into intervals and shows their frequency as bars. A tally chart counts discrete events in categorical rows. They look similar when complete , the Data Visualisation Catalogue notes that "the final result is similar to a histogram" , but they are conceptually different. The histogram's x-axis is a continuous scale; the tally chart's rows are independent categories. You cannot use a tally chart for continuous data (temperature, time-to-resolution) without first binning it, at which point a histogram is the correct form.

The one decision worth knowing: phantom group boxes (faint rectangles) are drawn before the marks animate in. This mirrors the pre-printed form structure of a physical tally sheet, where blank boxes exist before any data is recorded. The boxes also make the group-of-5 structure legible from the first frame , the viewer understands the encoding before a single mark appears.

FT Visual Vocabulary + Tufte FT Visual Vocabulary: Distribution , Frequency (closest match; tally charts predate most formal charting frameworks). Abela quadrant: Comparison , comparing discrete frequency counts across categories. Tufte: tally charts achieve near-perfect data-ink ratio , every mark is one data point .

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 tally chart in D3 v7. Two files:

The ideas in this chapter didn't appear from nowhere. Wilhelm Lexis was a 19th-century German statistician who developed the Lexis diagram , a coordinate framework for displaying demographic data by age and year , that essentially formalized tally-style counting into a 2D visualization. Wilhelm Lexis, circa 1900. AI-generated portrait based on a public domain photograph (Wikimedia Commons).

The ideas in this chapter didn't appear from nowhere. Wilhelm Lexis was a 19th-century German statistician who developed the Lexis diagram , a coordinate framework for displaying demographic data by age and year , that essentially formalized tally-style counting into a 2D visualization. Wilhelm Lexis, circa 1900. AI-generated portrait based on a public domain photograph (Wikimedia Commons).