Typical bar charts have issues with Fitts’s law for interactions. That is that the area of the bar prevents the user from easily moving from one bar to the other. Additionally when the bars are at some minimum area (or there is no area), the user may be unable to interact with the data.
This example ensures that there is a minimum interactive plane, in order to allow the user to always interact with a data point, even if the data produced has no display. This combats Fitts’s Law by ensuring that the area of the bar is above some bound, however the user still must adjust the cursor. See it in action on The Global Mail
Forked from Fitts’s Bar, I which allows the user to interact with only the x dimension in order to invoke a tooltip.