Jason Forrest delves into the history of a single Isotype and a bit of the general background on the picture language:
Isotype is a highly refined picture language designed for educating people with as few words as possible. Created by Otto Neurath in 1925, the International System of Typographic Picture Education (ISOTyPE) evolved over the next two decades with the collaboration of Marie Neurath and Gerd Arntz. The trio developed their distinct approach to data visualization iteratively, and very collaboratively. Otto provided the overall direction, Marie “transformed” the data to present the story, and Gerd designed the pictogram units and highly-refined designs.