Pie chart

A circular chart divided into sectors, with each sector’s angle or area representing a category’s share of a whole.

Central angle: The angle formed by two radii meeting at the center of a circle. Each sector’s central angle is its fraction of the total multiplied by 360 degrees.
Part-to-whole relationship: A relationship in which several components together make up a total. This is the specific relationship a pie chart is designed to display.
Bar chart: A chart that represents values with rectangular bars whose lengths are proportional to the data. Aligned bar lengths usually make close category values easier to compare than sector angles.
Nightingale rose diagram: A polar area chart popularized by Florence Nightingale to display monthly mortality data. Its sectors vary in area and connect pie-like geometry to a historical public-health argument.
Visual encoding: The mapping of data values to visual properties such as position, length, color, or area. Pie charts map category shares to sector angles and areas.
Proportion: A relation expressing one quantity as a fraction of another. A sector translates each category’s proportion of the total into part of a circle.
Categorical data: Data consisting of observations assigned to distinct groups or labels. Each sector typically represents one category’s contribution to the total.
Stacked bar chart: A bar chart divided into segments representing component values or category shares. It shows composition while allowing easier comparison across multiple groups.
Polar area diagram: A circular chart in which values are represented by sector areas, often through varying radii. It resembles a pie chart but encodes magnitude through radius as well as angle.
Chartjunk: Decorative or redundant visual elements that distract from a chart’s data. Three-dimensional effects and ornament can obscure sector comparisons.

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William PlayfairBroader topic: Playfair used the pie chart to compare components of a whole in his later statistical work.