From the International Atomic Energy Agency:
And a description of the scale: http://gnssn.iaea.org/regnet/Pages/INES.aspx
The tiers in this graphic are meant to represent increasing levels of severity for nuclear events, ranging from “anomaly” to “major accident.” A description states that “the scale is designed so that the severity of an event is about ten times greater for each increase in level on the scale.”
Yet neither the surface area nor the color used give readers a sense of the data being presented which, in this case, is the impact of a nuclear event. I’d go so far as to say the visualization, which claims to “facilitate communication and understanding…on [sic] the safety significance of events,” is misleading in these regards. Perhaps the creators worried that if they scaled the levels proportionally the end result would look uncannily like a mushroom cloud.
However, I haven’t been able to find a satisfactory, even useful way of visualizing seven degrees of magnitude in a graphic sized for a screen. Is there a way of doing so? Is a visualization even helpful in this situation?