Illustrate three variables that sum to 100 % in a triangle where coordinates are {x, y} and where the redundant third dimension y2 := 100 - x - y is depicted with gridlines and labels. This triangle is also known as the probability triangle, used to depict mixed strategies in games with three actions (e.g., "Rock, paper, scissors").

Example output (graphs/) can be reconstructed by evaluating the notebook SharesTriangle_Maker.nb

Example data (csv/) was retrieved from the World Bank on 2023-01-06, using handpicked API calls here: https://data.worldbank.org/indicator/SP.POP.65UP.TO
The classification into {children, working age, elderly} at age ranges {0-14, 15-64, 65-} is a bit loopy but follows a long tradition across statistical agencies.

Example plots depict the evolution of age group population shares in selected countries. Data from the World Bank (CC BY-4.0).

The preview plot shows the location of all data points inside the complete shares triangle. This can be useful for deciding on how to customize the shares-triangle plot.

In this shares-triangle plot some of the graph options were selected at the SharesTriangle_Maker.nb partly based on the look of the above preview plot. Option values that result in a useful graph depend on the data, for example how densely the plotted points are packed inside the triangle.