What is a safe neighborhood? How to use crime-mapping correctly

Once a week or so, I publish a report by RAIDS, an online tracking system used by Durham, that keeps track of all crime taking place within a one-mile radius of Ninth Street Shopping District. The latest of these reports, for example, shows that 29 criminal incidents took place in the area in the past 10 days. On the first brush, this sounds like a lot and, indeed, the RAIDS map of Durham shows our neighborhood in the shades of reddish yellow, which tends to indicate higher than normal crime rate.

Yet these statistics can be highly misleading. As good folks at Trulia have recently posted, just looking at the heat map of crimes tells you little about the relative safety of the area. The real question is not how much crime -- which is often dependent on the amount of commercial activity in the area -- but what kind 

of crime. When viewed through this lens, our area is a far cry from a criminal hotbed.

To illustrate, let's first take a look at the typical crime map of Durham's crime centered around Ninth Street. I took this data from Trulia Local. 

Looks bad, right? The red and the yellow colors denote high incidence of crime. But a surprising thing may jump out: Trinity Park, among the most affluent neighborhoods in Durham, is almost entirely colored in reddish/yellowish colors. But is this right? Most locals would argue that the area surrounding East Campus of Duke is fairly safe, a province of palatial homes of Duke faculty and expensive student housing. Indeed, when parsing through the data, one discovers that almost all of the incidents are related to partying as opposed to assaults. Similarly, the dark red areas enveloping Ninth Street Shopping District is theft related, which is unsurprising given the high volume of commercial activity going on there.

Now, let's take a look at the same map now showing the ratio of violent-to-nonviolent crimes. Here, we count crimes such as shootings and assaults as “violent” while petty crimes such as vandalism or theft are “nonviolent.”

Not much going on, particularly when compared to South-East and Central Durham which has seen an unfortunate rash of violence in the past year. 

To make comparison even more explicit, let's see a side-by-side of typical crime map of the two areas:

East Durham Crime Map

Although the East Durham map is redder, it is not dramatically different in color saturation. But what a contrast when the ratios of violent vs. non-violent crime are taking into account. As shown above, this ratio presents a far more  accurate picture of safety in an urban neighborhood.

Trinity Park Crime Map

As with most things in life, the simple and most "common sense" impressions are often wrong or incomplete. Just as one does not compare apples and oranges, one should not simply compare the crime level of a generic car-oriented suburban neighborhood to its urban counterpart. Instead, it is  

    imperative to look at what crime takes place and 

    whether this crime is an inherent outgrowth of 

    proximity to commerce or an indication of  

   something more sinister.