Venn diagram

Use a Venn diagram when the question is how many items two or three groups share. Use a bar chart for more groups.

Web and email readers overlap the most

Readers by channel, a row for each set and each overlap, illustrative counts

EmailAppWeb

This chart cannot be displayed here: it needs JavaScript and WebGL.

circle areas are the sets' totals and each pair's overlap is drawn at its size; the overlap of three is where the geometry puts it

The same chart in each style

Source

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Rich Markdown

```chart
type: venn
title: Web and email readers overlap the most
subtitle: Readers by channel, a row for each set and each overlap, illustrative counts
data:
  inline:
    - {channel: Email, readers: 620}
    - {channel: App, readers: 480}
    - {channel: Web, readers: 540}
    - {channel: "Email & App", readers: 180}
    - {channel: "Email & Web", readers: 210}
    - {channel: "App & Web", readers: 150}
    - {channel: "Email & App & Web", readers: 70}
encoding: {sets: channel, y: readers}
axes:
  y: {label: Readers}
```

Fields that matter

type: venn with encoding.sets for the sets a row counts and encoding.y for its size
A set is a row with one name and gives that set’s total; an overlap is a row with two or three names joined by & or a comma, such as Email & App, and gives the size of that overlap, including whatever else lies in it; a list of names is read the same way
Every set needs a row of its own; two or three sets are drawn, and four or more fail with a reason
Circle areas are proportional to the totals and each pair is placed at the distance at which its overlap has the size given, so areas are exact for two sets, and for three sets only when the three pair overlaps fit together; when they do not, a warning says so and a note names the overlaps as drawn off size; the overlap of three is wherever the geometry puts it, and a note says so
An overlap cannot be larger than a set or a smaller overlap it lies in; an overlap of zero draws the circles apart
The shares in a readout are computed by RichView and marked as derived; a name that does not fit inside its circle is left to the legend and reported
encoding.facet makes one diagram per value on one scale; axes.y.label names the size

Interactions

Hover or focus a circle or an overlap to read its size and the share of each set.
Click a legend entry to remove a set and back.
Open the Table view, Download PNG or CSV, or Expand the chart.