Police departments across the country are gearing up for a late night this December 31st, one on which they’ll especially be on the lookout for drunk drivers.
Looking at 10 years worth of data reveals that some areas of the country are more prone to traffic fatalities due to intoxicated driving than others.
John Nelson with IDV Solution’s UX Blog who created the map said that he was both surprised by the percentage of fatalities where alcohol was a factor and how it varied regionally.
“This map is an effort to better understand the geographic characteristics of these events, particularly the regional dimension that that intoxication plays [...],” Nelson wrote. ”It turns out, some areas are much more well behaved in this regard than others.”
Here’s how Nelson described putting together the map:
The hexagonal mesh is one way of more fairly visualizing highly overlapping, highly clustered, data (pretty much wringing point data into a polygon choropleth map where ratios can be calculated). The nature of our population distribution and our transportation infrastructure leads to traffic fatality data points that are highly stacked upon each other. Each of these incidents represents a horrible event and to paint in the raw data in a way that would obscure them would be unfortunate -and ineffective. The mesh carves up the country into a baseline set of place-buckets (more uniform than political boundaries) of roughly equal size into which the overall number of fatal crashes is aggregated, and within which a rate of intoxication can be shown.
How to be true to the underlying population? Once the overall number of events within each zone is added up, the visual for that zone can be scaled accordingly (a way of un-biasing the uneven populations) so that areas with lots of events appear larger and areas with fewer events appear smaller -and areas with no events disappear entirely.
Here’s a close up of the map’s key:
To be clear, the map as a whole does not show only traffic fatalities due to intoxication. It is color coded to show the percentage of traffic fatalities due to drunk driving.
As Nelson put it, “the coloration of the zones is tied to the rate of events that involved intoxication.”
Nelson pointed out some areas have “impressively” low rates of traffic fatalities due to intoxicated driving, like Memphis and Manhattan, while other areas like St. Louis and “pretty much all of South Carolina” have high rates.
Find more about the maps, including larger, more detailed sizes on Nelson’s blog here.