Wednesday, July 24, 2013


Longtime readers of the Director's Desk have been bored stiff from time to time with my ruminations about such topics as evidenced-based policing, situational crime prevention, and the like. Of particular interest to me is a phenomenon that is at the heart of a lot of good police work: digging into crime where it actually occurs--particularly impacted neighborhoods, blocks with pernicious problems, specific addresses with repeat offenses, even an individual apartment.You will find lots of examples here in my blog about problem-oriented policing strategies that are targeted at these micro-places.

A friend is the co-investigator on several research projects that have involved crime hot spots.  One of these that caught my attention last year was a study of juvenile crime in Seattle. The reserarchers, Drs. David Weisburd, Elizabeth Groff, and Nancy Morris, found that a huge percentage of juvenile crime occurs on a very small percentage of the block faces in Seattle (a block face is both side of one street, between the two adjacent intersections--like the 1500 block of S. 9th Street.)

I've been meaning to look at this in Lincoln for some time, and I got motivated yesterday to do so, a job that took about 15 minutes to set in motion, and ran on my computer while I was away at lunch.  Here's my method:  I took all the crimes reported to LPD in 2012 (21,153 total), and joined those points to the nearest street segment.  Street segments in our geographic information system are essentially the equivalent of the block faces studied by Dr. Weisburd, et al. in Seattle. I then summarized the crimes by street segment, and joined the results back into the streets layer. My result was a GIS layer of streets, where each segment also has a COUNT field that is the sum of the 2012 crimes along that segment.  Here are the results:

There were 13,771 total street segments in the City of Lincoln.  Of those, 7,481 (54%) had no crime at all in 2012. Moreover, 81% of all the crime (14,149 offenses) occurred on only 5% of the street segments (689 segments). The top 1% of the street segments (138 segments) accounted for 7,148 crimes--41% of the total.

These data are consistent with other studies, and demonstrate something very clear: crime is intensely concentrated at these very local micro-places. Police efforts focused on intervening in the conditions and preventing crime at individual premises on those blocks where crime is concentrated are far more likely to be effective than driving around aimlessly burning fossil fuel (or as we call it in policing, "routine patrol").

Here's a snapshot of the 5% of the street segments in Lincoln where 81% of the crimes occurred in 2012.


Herb said...

Interesting to see the high schools all included. Any way to then take this information and create a heat map, showing even further density/number of occurrences?

Tom Casady said...


Certainly. In fact, a continuous surface "heat map" would probably be the most common way a crime analyst would depict the relative density of crime in a City. A third way would be to create a choropleth map, in which a color ramp would be applied to a polygon layer like police reporting districts or census block groups, based on the number of crimes within each. A fourth way would be to use graduated symbols, in which addresses are depicted with circles whose sizes are based on the number of crimes at that address. All of these methods have some advantages and disadvantages.

Steve said...

The question in my mind is, will targeting the high-crime areas actually reduce crime overall, or will it simply move to other areas? Or, should we focus on protecting the areas that are relatively crime-free so as to keep it from spreading?

Mr. Wilson said...

Is it possible to run a historical version of this analysis? It would be fascinating to see how the concentration of crime has changed (or not) over time.

Anonymous said...

Looks like the Near South is still a hotbed... do you see any evidence our neighborhoods program is working there?

Anonymous said...

NPR featured a story about police using software to predict where crime will occur in the future by analyzing past crime trends. Is this something Lincoln would consider?

Tom Casady said...

Mr. Wilson,

Yes. I'll do that sometime.


Yes, this area has stabilized, although it' never going to look like Wilderness Ridge.


Click "crime analysis," "GIS", or "technology" in the label cloud, and I think you'll see that we are pretty much on the leading edge of such technologies. While we don't use the specific software touted in the NPR story, we have others in the same genre.

Tom Casady said...

Mr. Wilson,

If I had the time, it would be pretty cool to create an animation like this!

Anonymous said...

"If I had the time..."

That's why they make unpaid undergrad interns!

Nikolas said...

Higher concentrations of crime at particular street segments may represent actual higher crime, but could also reflect factors such as higher residential concentration, greater resident vigilance, or greater police patrol presence. Isolating and mapping more serious offenses, rather than mapping them together with less serious offenses, might also reflect the severity of crime and risk to residents more accurately.

All of that said, I think it's quite exciting to see mapping technology being applied in this matter. I'm very glad you shared it. Now, how can we use this to improve the city? Targeting these areas might reduce crime, but without controlling for other variables it's quite possible that it will merely increase the reported crime rate instead.

Tom Casady said...


There is a good body of research on the displacement of crime. In a nutshell, no, efforts to reduce crime hot spots do not result in merely moving those hot spots to other locations.


You are quite correct on all these points.

This is just a tiny example of how we use GIS technology in crime analysis, but it points out a very important point: most blocks have no crime at all; some blocks have a lot of crime; a huge percentage of all crime is on a tiny percentage of all blocks. The implications are obvious: spend your time where the problem exists, and focus your proactive efforts there.

Mr. Wilson said...

@Tom Casady Yes, that would be awesome! Boy, I would have loved to have had access to data like this back in my grad school days.