Localized spread of measles in United States has received unprecedented coverage in recent weeks. Lack of vaccination in certain communities has been cited as the reason for several outbreaks this year.
While, many articles have tried to drive home the point that vaccines indeed work, none have been as clear as this chart published in Wall Street Journal.
This simple heatmap shows that the number of measles cases (per 100K persons) significantly declined across all states after vaccines were introduced.
The visualization is every effective in showing the spatial & temporal variation in outbreaks and shows that vaccination was effective in almost eradicating measles in every single state.
This is a great example of enabling clarity and bringing out the key takeaway from the data through visualization.
Caveat: The context should always be kept in mind when choosing a visualization framework. The same chart would have been totally ineffective if there was not enough visual separation after the introduction of vaccines.