*Because of rounding, these totals do not add up to 100 and 360.
The size of each central angle is proportional to the size of the corresponding quantity, here the number of seats.
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.
Playfair thought that pie charts were in need of a third dimension to add additional information.
In a pie chart, the arc length of each slice (and consequently its central angle and area), is proportional to the quantity it represents.Playfair presented an illustration, which contained a series of pie charts.One of those charts depicting the proportions of the Turkish Empire located in Asia, Europe and Africa before 1789.Often used for aesthetic reasons, the third dimension does not improve the reading of the data; on the contrary, these plots are difficult to interpret because of the distorted effect of perspective associated with the third dimension.The use of superfluous dimensions not used to display the data of interest is discouraged for charts in general, not only for pie charts.This invention was not widely used at first; The French engineer Charles Joseph Minard was one of the first to use pie charts in 1858, in particular in maps.