Initially I got really excited when I heard about Trulia launching crime maps yesterday. If during your home search you’ve ever tried researching the crime in your prospective neighborhood you’ve probably encountered a great deal of frustration. The reason is that the data has never been easy to look at or interpret. It’s often so granular to be useless – e.g. specific crimes at specific addresses on specific dates. Even the summary data is often only aggregated at the level of 2 weeks – hardly a meaningful time period.
So when the news hit about Trulia’s new feature I immediately pulled up the Chicago crime map shown below.
After you study it for a few minutes it drives home the challenge of trying to figure out if a neighborhood is “safe” using all the available data. What’s wrong with this picture? It displays the number of incidents per block per year. Therefore, all else being equal, densely populated areas get penalized because they have more people per block and are therefore more likely to have crime. More people = more victims = more criminals = more crime. In the map above some of the most desirable parts of the city are glowing red – River North and the Loop for instance.
Not to mention that these crime maps are in beta so they don’t quite work as you’d expect. For instance, changing what crimes you want to look at does not seem to change the map. But that would be easy for Trulia to fix.
What you really want to look at is the number of crimes per resident per year. I’ve done this analysis of Chicago crime as a percentage of population before and it makes a lot more sense. However, a) my data is a bit old (been meaning to update it) and b) I can only do it at the official Chicago community area level and c) there are even flaws in that methodology. Regarding this latter point, check out property crime for the Loop. It’s off the chart. And the reason is probably because every day people pour into the Loop (they don’t live there) creating lots of crime opportunities. So the “effective population” of the Loop is much higher than the numbers suggest – i.e. my denominator is understated and hence the percentage is overstated.
I wish I had a better answer for people trying to determine if a neighborhood is safe but sometimes the only thing you can do is drive around at different times of day and see if you like the feel of the neighborhood. One warning sign would be a lot of young adult males loitering on the street in the middle of the work day. Under employed males = more crime.