When should I use a unit chart?

Making small counts feel tangible (e.g., 1 icon = 1,000 people) ● Showing part-to-whole ratios like survey results or risk

When should I avoid a unit chart?

When counts are very large (too many icons to render) ● When precise numeric comparisons are needed

What are common mistakes with unit charts?

Using inconsistent icon sizes that distort perception ● Not stating the unit-to-value ratio clearly

Part-to-Whole

Unit Chart

Represents each data point as an individual icon or shape, making counts tangible and part-to-whole ratios intuitive.

Patient Outcomes

1 square = 1 patient (N = 100): 60 Recovered + 25 Improved + 10 No Change + 5 Worsened

View data (4 rows)

Chart data table: Patient Outcomes
Count	Outcome
60	Recovered
25	Improved
10	No Change
5	Worsened

Make a unit chart with your data

Use a unit chart when…

Making small counts feel tangible (e.g., 1 icon = 1,000 people)
Showing part-to-whole ratios like survey results or risk

Avoid when…

When counts are very large (too many icons to render)
When precise numeric comparisons are needed

Data it needs

Property	Value
Min Rows	2
Min Columns	2
Column Types	stringnumber

Visual anatomy

Marks

icon / square

Channels

color (category)count (quantity)grid position

Axes

Guiding principles

Consider instead

Parliament Chart

When showing seat/vote distributions

Sunburst Chart

When hierarchical composition is the focus

Common mistakes

Using inconsistent icon sizes that distort perception
Not stating the unit-to-value ratio clearly

History

Isotype charts, created by Otto Neurath in the 1930s, are the direct ancestor of modern unit charts.

Accessibility notes

State total count and breakdown per category in text; avoid relying solely on color.

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