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  • Writer's pictureJason Gravel

Viz of the week - Open and Concealed Carry laws in the US

For the last few months, I've been working on different grant proposals and papers that deal with gun laws in the United States. Thankfully, in recent years, researchers have come up with great databases that are literal one-stop-shops for folks interested in gun policies. For example, Michael Siegel and his colleagues at the Boston University School of Public Health have come up with an amazing website where they document different types of state laws related to firearms. They cover state laws between 1991 and 2019 allowing us to track changes over time, which is pretty neat. You can also select among several law categories and see the number of laws each state has implemented each year. True to their public health roots, they also provide information about gun-related death for each state. Of course, you can also download the whole dataset in csv format! 

The main advantage of using the Boston University dataset is that laws are categorized into standardized categories. This is great when you are trying to create a longitudinal dataset consistent across states and time. Of course, this categorization comes at the expense of precision. Gun laws are extremely complex; every state uses its own jargon and includes its own quirky provisions. Sometimes you are interested in a very specific aspect of a law, which means that you have to bite the bullet and comb through 51 different legal codes...

Well, before you do that, you should check out RAND's ever-evolving State Firearm Law Database. The database is the result of the herculean efforts of Samantha Cherney, Andrew R. Morral, Terry L. Schell, Sierra Smucker, and (I assume) an army of RAND staffers. This is as thorough as it gets folks! 

The database, which is available to download, includes about 2240 state firearm laws implemented, modified, repealed, or just absent. It covers with precision the years 1979 to 2019, includes handy labels indicating whether the legal change is "Permissive" or "Restrictive", and includes relevant citations to legal statutes and cases. The downside of using the RAND database is that, unlike the Boston University dataset, the categorization is less systematic. This, of course, reflects the researchers' efforts to create a more comprehensive, albeit more complicated database. The RAND dataset is more specific and perhaps a little richer, but using it might require you to come up with your own classification to group together. (or not) labels like "Carrying a concealed weapon (CCW) - shall issue protective order", "Carrying a concealed weapon (CCW) - shall issue", and "Carrying a concealed weapon (CCW) - shall issue (permit not required)". You may or may not care about the distinctions between those varieties of "Shall issue" laws. 

For my purposes, I just wanted to visualize changes over time in how restrictive states were on open carry and concealed carry laws. RAND has created a neat widget to scroll through changes in "carrying a concealed weapon" laws, but I needed a graphic that would show me these changes in a single figure, for both open carry and concealed carry laws. So I created a heatmap using Seaborn a Python data visualization library built on top of matplotlib. The plot has two rows for each state: the top row reflects changes in open carry laws (for handguns), the bottom row reflects changes in concealed carry laws. Each column represents a year between 1991 and 2019, and the cells of the resulting matrix are colored to show the status of each law, by state, and by year. 

For open carry laws, I preferred the simpler coding scheme used by the Boston University database. However, I wanted to differentiate between "Shall Issue" and "May Issue" for concealed carry laws, which was easier to differentiate using the RAND dataset. And so here it is! A quick reference guide on these laws over time:

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