Pie chart

In a pie chart, the arc length of each slice (and consequently its central angle and area) is proportional to the quantity it represents.

The earliest known pie chart is generally credited to William Playfair's Statistical Breviary of 1801, in which two such graphs are used.

[10] Florence Nightingale may not have invented the pie chart, but she adapted it to make it more readable, which fostered its wide use, still today.

[12] Nightingale's polar area diagram,[13]: 107  or occasionally the Nightingale rose diagram, equivalent to a modern circular histogram, to illustrate seasonal sources of patient mortality in the military field hospital she managed, was published in Notes on Matters Affecting the Health, Efficiency, and Hospital Administration of the British Army and sent to Queen Victoria in 1858.

[citation needed] This type of circular graph can support multiple statistics at once and it provides a better data intensity ratio to standard pie charts.

The first known use of polar area diagrams was by André-Michel Guerry, which he called courbes circulaires (circular curves), in an 1829 paper showing seasonal and daily variation in wind direction over the year and births and deaths by hour of the day.

The second set is represented by the superimposed polar area chart, using the same angles as the base, and adjusting the radii to fit the data.

For example, the base pie chart could show the distribution of age and gender groups in a population, and the overlay their representation among road casualties.

Age and gender groups that are especially susceptible to being involved in accidents then stand out as slices that extend beyond the original pie chart.

The table lists the number of seats allocated to each party group, along with the derived percentage of the total that they each make up.

In the example, the central angle for the largest group (European People's Party (EPP)) is 135.7° because 0.377 times 360, rounded to one decimal place, equals 135.7.

A flaw exhibited by pie charts is that they cannot show more than a few values without separating the visual encoding (the “slices”) from the data they represent (typically percentages).

[7] Statisticians generally regard pie charts as a poor method of displaying information, and they are uncommon in scientific literature.

[25][26] In a pie chart with many section, several values may be represented with the same or similar colors, making interpretation difficult.

Pie chart of populations of English native speakers
In a redrawing of the perspective pie chart shown at MacWorld 2008 (top), the smaller Apple slice appears larger than the Other slice – the 2D pie chart (bottom) gives the true picture
Information about the data as a whole in the center of a doughnut chart
Exploded pie chart for the example data (see below), with the largest party group exploded.
" Diagram of the causes of mortality in the army in the East " by Florence Nightingale.
Like conventional pie charts, a variable-radius pie chart has wedges whose areas represent total quantities in respective categories/groups. However, here, each radius represents an amount of that quantity per unit within that category. In this example, each wedge's area represents total CO 2 emissions of all people in that category, and each radius represents emissions per person within that category.
Multi-level pie chart representing disk usage in a Linux file system
A spie chart comparing number of students with student costs across four different schools
Square pie chart (waffle chart), showing how smaller percentages are more easily shown than on circular charts. On the 10x10 grid, each cell represents 1%.
A pie chart for the example data
3D pie chart showing Atmospheric air components percentage
Three sets of percentages, plotted as both piecharts and barcharts. Comparing the data on barcharts is generally easier.
An example of a pie chart with 18 values, with some colors repeated
An example of a doughnut shape pie chart, showing the batting and run records of Indian cricket players in test matches in 2019