The New York Times features a map that depicts the average number of daily new cases in each county across the U.S. in the past week, and shades each county by how many cases it has per 100,000 people. White and light yellow are good; and low, and orange, then red, and then dark maroon indicate higher numbers of cases per 100,000 people.
Right now, the map features a horrific red-orange mitten that makes up most of the state of Michigan, a similar patch of red and orange in the Texas panhandle, and some ominous blotches of orange in Minnesota and around the New York City area. Grant County in Oregon stands out as the darkest spot in the west, albeit with a mere 7.1 average cases per day. (That’s what happens when you’re one of the least-populated counties in Oregon.)
In fact, the orange and red portions of the Texas panhandle appear to be mostly similar circumstances of outbreaks in largely rural counties where communities are few and far between. Carson County is averaging 12 new cases per day, Garza County 9.9 cases, Cochran County 5 cases, and Briscoe County 1.7 cases. Motley County, Texas, rates the red color with just 1.1 average new cases per day. That’s what happens when a county has just 1,200 people or so; even a small outbreak can generate a figure that calculates out to 95 cases per 100,000 people.
A small outbreak in a sparsely populated county still isn’t good news, and it’s worth noting that some of these red and maroon counties aren’t just a matter of normal-sized outbreaks in small populations. Gray County is at 34 cases per day, Hockley County is at 39 cases per day, and Hutchison County is at 45 cases per day.
But those sparsely-populated Texas counties end up shaded the same ominous colors as ones in Michigan like Saint Clair County, which is averaging 263 new cases per day, Oakland County which is averaging 922 new cases per day, and Wayne County, averaging 1,457 new cases per day.
In one sense, it makes perfect sense to measure outbreaks per 100,000 people; more populated counties are going to have a higher number of cases than sparsely-populated ones. But an outbreak of about eight new cases in a week in Motley County, Texas, is just not as worrisome as more than 10,000 new cases in week in Wayne County, which includes Detroit. A data-visualization system that treats the two situations equally obscures and muddles the facts as much as it attempts to illuminate them.