According to sociological research, young African-American males in urban areas are the largest category of homicide victims, and most of these victims are killed by people with similar demographic characteristics. Gun violence tends to occur between gang related networks, and these networks have a localized monopoly over crime. In Boston, for example, 66% of street robberies occur on 8% of streets.
As part of Project Longevity, Michael Sierra-Arevalo has mapped out gang activity and crime in New Haven, finding that gang territory tends to overlap pretty strongly with homicides and armed robbery. I wanted to test that theory out in another location. Chicago, for quite a while, has been known for their gangs: the Gangster Disciples, Black Disciples, Vice Lords, and the Black P Stones have been around for over half a century. Gang turf tends endure generations. Here's a map of the gangs in Chicago in the 1980s:
And here's a map of updated 2011 data:
They're pretty similar.
Luckily for me, the city of Chicago has also created a publicly available data set of all the crimes and homicides since 2001. (That, and other interesting data on the city, can be found here). I downloaded a few of these data sets, subsetted for armed robbery and homicides, and plotted their coordinates on a satellite image of Chicago:
As you can tell, there is significant overlap between robbery and homicide locations. And, when you compare the plot to the map of Chicago gangs in 2011, the overlap tends to occur in gang turf.
I also went ahead and downloaded the data set about drug arrests since 2001. Depending on the description of the arrest, I categorized the police reports into the drugs involved, and plotted them with the following colors:
- Cannabis/Marijuana = Yellow
- Cocaine = Brown
- Crack = Coral
- Heroin = Cyan
- Barbiturates = Bright Green
Weirdly, marijuana and crack arrests seem to happen pretty uniformly around the city. Cocaine and barbiturates arrests are few and far between. Heroin arrests, on the other hand, seem to be pretty condensed and restricted to certain areas of the city. Referring back up to the 2011 gang map, these heroin areas look kind of similar to gang areas, but not too much so. It's definitely not as obvious of a relationship as with gang activity and homicide and armed robbery, which is interesting.
Going forward, I'm looking to break down the data by year -- if we assume gang turf is related to homicides and robberies, do we also notice that rates of homicides and robberies in certain beats tend to persist year after year? Do certain areas improve in terms of homicide and robbery rates? How does gang turf relate to city housing projects (presumably that data is also available somewhere)? Expect more to come!