Mosaic plot

Mosaic plot showing cross-sectional distribution through time of different musical themes in the Guardian's list of "1000 songs to hear before you die".

A mosaic plot, Marimekko chart, Mekko chart, or sometimes percent stacked bar plot, is a graphical visualization of data from two or more qualitative variables. It is the multidimensional extension of spineplots, which graphically display the same information for only one variable. Although the term spineplot was originally used by Hummel to describe univariate graphs, Cox points out that the term has also been broadly applied to displays of two or more variables.

The mosaic plot makes it possible to visualise relationships between different categorical variables. For example, independence is shown when the boxes across categories all have the same areas. Mosaic plots were introduced by Hartigan and Kleiner in 1981 and expanded on by Friendly in 1994. Mosaic plots are also called Marimekko or Mekko charts because they resemble some Marimekko prints.

As with bar charts and spineplots, the area of the tiles, also known as the bin size, is proportional to the number of observations within that category. Although mosaic plots most commonly show the relative frequency of each combination of values, they can also be used to display the goodness with which a loglinear model fits the data.

Mosaic plot construction is described and illustrated in detailed worked example by Jeppson and Hoffman using the ggplot2 package in the R language.