Thursday, August 22, 2013

Not quite as intense

Last month, I wrote a post called Micro-places in which I tried my own version of some research that studied how crime concentrates in very small places: in this case, a study of individual blocks in Seattle. My little project basically looked at the same thing in Lincoln, and showed similar results: intense concentration of crime on the "top blocks."

The post was certainly not my first about the geographic dynamics of crime in Lincoln, but for some reason, it got more attention than most, as evidenced by the online comments, and also by a few delivered to me personally. One of those came from a city council member, who correctly perceived that a lot of those "hot blocks" were in retail areas.  This is really pretty obvious when you think about it.  Many common crimes are related directly to retail activity (shoplifting, credit card fraud, forged checks, etc.), and many are related to the processes that bring people together in the same place at the same time: potential victims and potential criminals--something that happens naturally around busy retail areas.

The council member wondered if the picture would be different if I had excluded those retail-oriented crimes. I opined that it would, but I have my own formula for assessing such questions, something I call the "neighborhood well-being incidents." My 2004 intern, Becky Colwell, won a national student paper competition using this concept, which she named the "quality of life index." What Becky and I did was rethink the kinds of police incidents that most accurately reflect the safety and well being in a neighborhood.

Becky's paper describes this in greater detail, but in essence we thought that some crimes had very little impact: a fraudulent credit card swipe at the grocery, a shoplifted pack of cigarettes at the convenience store, a resident of the youth detention center assaulting a staff member.  Other crimes would more obviously influence the quality of life or the well being of the neighborhood: a residential burglary down the street, a child abuse in the apartment building, a drug arrest at the park, etc.. Using combinations of incident codes and location codes in the police database we excluded the kinds of crimes at places that seemed to have little relevance to well being, which in the process also emphasized those that do.

I ran the same GIS process as in my earlier Micro-places post, but this time filtering the incident and location codes using my neighborhood well being query. The resulting map is below, and a side-by-side comparison will show some similarities and differences. The key difference, though, is not really depicted by the map so much as the data. The neighborhood well being incidents are not nearly so concentrated as crime generally. Removing the retail and institutional crime reduces the intensity of the concentration. Whereas 81% of all crime was concentrated on the top 5% of the blocks, when only neighborhood well being incidents were examined, 49% of those incidents were concentrated on the top 5% of the blocks. That's still some major concentration, nonetheless. Some of that is simply a byproduct of population density, some is related to economic and demographic conditions, and since many crime types are integrally related to our automobile culture, traffic density is another important factor in concentrating crime along certain street segments.

No comments: