Better data visualization: Why are Coronavirus maps on the news so unhelpful?

Spring 2020: we are under a stay at home order because of the coronavirus. I can’t comment on the medicine side but one thing I definitely think could be improved upon is the communication about the unprecedented actions being taken to stem the virus. To be fair this is a very tough challenge — many governments have clearly been caught flat footed — yet news organizations aren’t obviously doing any better. As I watch the Canadian, US, and UK news I’m not sure any are covering themselves with glory.

Take for example a chart that we have seen a lot of on US cable news: coronavirus cases in the US by state. Despite this being shown on many major news outlets I have been left wondering what its purpose is.

Scott Berinato has a book on how to present information visually: Good Charts. This contains useful information and checklists on making effective, i.e. persuasive, data visualizations. Relevant to the topic at hand Berinato (2016) talks about why some geographic mappings may be deceptive. “The size of geographic space usually over- or under-represents the variable encoded within it. This is especially true with maps that represent populations.”

What about the map of coronavirus cases in the US by state? This map seems like a reasonable representation of the data that we have. (For the sake of this discussion, given my lack of specific knowledge, I will assume that the data has some value and deliberately ignore important differences in testing between states which almost certainly distort the data). The map being shown on cable news colour codes by number of cases; those states with a higher number of cases are indicated by a more dramatic shade.

Firstly, let me note that this map could be useful in certain circumstances. Assume that you were the US federal government and your aim was to help recovery by directing limited federal aid to states in most need. (I’m hoping that is their aim.) If you were sending aid you might want to know which states have the highest number of cases to send them the needed supplies. (Technically I’m guessing you need to know what the numbers of cases are going to climb to by the time the aid arrives, but current cases might be a reasonable place to start). To this end the map might be useful as it tends to show lots of cases in states with large populations and populous states will generally need more equipment given they have more people.

That said do any of the cable news viewers find information on cases per state particularly useful? I would argue less than you might expect. It is certainly likely to worry people in the big states given the dramatic shades representing their states. This might help drive viewership in big states. That said, if your aim is not to worry but instead to inform one might expect viewers would be better served if they were told how badly their states are hit. To represent this, cases per head of the population might be a much better measure. The problem with the map based upon raw numbers per state is that it is conflating two different things: 1) how badly the state has been hit and 2) how big the state is. It is hardly surprising that California has a lot more cases than North Dakota, wouldn’t we all have predicted that absent any testing?

It is important to note that some of the differences between states will reflect genuine differences between how hard each state has been hit. It is intuitive that states with big cities which visitors travel to from all over the world and in which people live in close proximity might face special challenges, e.g., New York City. That said, we don’t want to give the impression that coronavirus is a problem just for the big cities or populous states. The chart that we see on the news has the great danger of confusing genuinely harder hit places with places than have more people. This feeds a problem in US public policy.

Unfortunately there appears to be somewhat of a divide in US public policy. Blue (Democratic leaning) states are generally taking more action against the virus than red (Republican leaning) states. This is a source of frustration to many commentators that I see on some news channels such as CNN, MSNBC, but I would argue that these channels are at least somewhat fueling the problem.

The challenge is that blue leaning states tend to have more people. (This is why Donald Trump’s election victory of 2016 looks more dramatic when shown on a map. I’m not making a point about the electoral college but that low density population areas tend to vote Republican meaning more space is coloured red on the map of the US than votes alone might imply). What does the map of coronavirus cases based upon infections per state do? It distorts what I’m assuming most viewers are interested in – the rate of infection in their state – and instead gives us raw numbers. The visualization being used on the news makes the virus look more like a problem focused on blue states than it truly is.

For example, the cable news map, which is similar to one used by the CDC, makes California look like it has a similar problem to Louisiana. (The last raw data I saw said reported cases of Covid 19 are similar: California, 15,865, Louisiana, 16,284). The problem is that Louisiana is a much less populous state than California, with just a little more than one person for every ten in California. Louisiana, currently, has a lot bigger problem per head than California. Given the west coast state has many more people this means your chance of being sick with coronavirus, all else equal, is much lower in California than Louisiana. Furthermore, assuming California has many more medical personnel and equipment given its greater population, the medical infrastructure of Louisiana is likely under much greater stress. The map makes it seem like California and Louisiana are in the same situation but they really aren’t (currently at least).

The chart makes it look like less populated states have less to worry about relative to more populated states, and we know that these less populated states tend to be politically redder. Some news organizations are disappointed with red states for not taking sufficient action but the visualizations they are using to illustrate the problem of coronavirus are the very ones I would use if I wanted to discourage red states from taking action. To be clear I’m not saying the US partisan divide will go away if CNN uses a better map but I don’t think the cable news networks should be fueling the problem and then complaining about it.

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Read: Scott Berinato (2016) Good Charts: The HBR Guide to Making Smarter, More Persuasive Data Visualizations, Harvard Business Review Press, Boston, Massachusetts