- To protect individuals' privacy, the CDC does not report counts in counties with low numbers of deaths. The number of deaths in Franklin County and Nantucket County fall below this threshold, hence they are absent from the above map.
- The rates of almost all causes of deaths vary with age. Age adjustment is a technique that removes the effects of age from crude rates and allows meaningful comparisons between populations of different age profiles. See the CDC's description of the process here.
- The map shows rates not raw counts. See the wikipedia entry on choropleths for the justification.
I am surprised that the death rate from drug overdoses is so high on Cape Cod (Barnstable County). The simplistic reading of the opioid crisis usually associates it with deprivation and poverty; the typical narrative does not particularly associate the crisis with affluent or vacation communities. But Barnstable's age-adjusted opioid death rate of 53.8/100,000 puts it at about 2.5x the national average A couple of technical points: