If you live in North Carolina, chances are you have to get your vehicle inspected each year, before you can renew your license plate. The inspection consists of a safety portion, and in some counties an emissions portion. In the past, 48 of NC's 100 counties required the emissions portion of the inspection - but as of December 1, 2018 only 22 counties require the emissions test. Follow along to see which counties!
But before we get started, here's a picture to get you into the mood. This is my friend Thelma's car, getting worked on in her dad's shop. Do you think it will pass the NC emissions test? That's kind of a trick question - since it's 1995 or older, it doesn't require an emissions test (because most cars older than 1995 don't have the standard OBDII emissions monitoring). Can you guess what year, make, and model her car is? Here's a hint - think 'Supernatural'! (leave your guess in the comments section)
Now, let's get to that emissions testing data. The NC Department of Environmental Quality (DEQ) website provides a text list of the 22 counties that now require an emission inspection as part of their annual inspection. A text list is OK for some things (for example doing a text-search for a specific county), but it takes a lot of effort to read through the entire list, and you don't get to see the geographical trends in the data.
To augment the text list, I decided to also present the data in map form. Here's my map, showing the 22 counties that now require the emissions inspection (in blue). If you're familiar with NC, you'll notice it's mostly the counties around the larger metropolitan areas (with more vehicles and more pollution), most of which lie along our major interstates (I-85 and I-40). Click the map below to see the interactive version, with mouse-over text showing the county names, and you can then click on the counties to find a list of inspection stations in that county.
How does that compare to the 48 counties that required an emissions inspection before the change? I'm glad you asked! I created a map of those too. That's quite a change, eh!?!
A map adds a whole new dimension to the data, that a list of counties in a text paragraph just can't provide, eh? What other analyses (graphical, statistical, etc) do you think might be useful to apply to this data?
If you're a SAS programmer, and would like to see the code I used to generate my map, here's a link. This particular example uses some features not currently available in Proc SGmap yet, therefore I used Proc Gmap to generate the map.