Friday, November 19, 2010

DC crime map - by block!

Ok this should be great, but on closer inspection it actually sucks.

My thoughts on first look: "Wow! I've still been going off this old homicides map because I haven't yet seen anything more precise. But block-by-block is amazing!"

But then I realized it's just a simple count of crimes for each block, not at all taking into account the size or population of the block. Hence universities, whose entire campuses count as one block, seem like the most dangerous places in the city. And then there's more obvious (and just dumb) examples like this pinwheel centered on Thomas Circle.
I don't think I'll be much safer on the small-slice blocks. In fact I think there's a good chance all eight blocks have statistically the same crime rate. If you measure it in a more meaningful way, that is.

So yes, in reality it's not useless. I've seen some interesting things when comparing blocks of similar size. But it's pretty frustrating. Because the DC Crime Policy Institute it comes from gives no info that would help better interpret the data. And because the information they give us is already divided into bins (5-9 crimes/year, 10-25 crimes/year, etc) you can't manually correct for block size with any accuracy.

There's several easy steps they could've taken to produce a better (not perfect) representation of crime in The District. The easiest thing to do would be to simply divide the number of crimes by the area of the block. Then at least they wouldn't have made a map that was near-meaningless.

I guess since that would be so easy, the only conclusion I can come to is that the map was mostly decoration and what they were most interested in was the data in their table showing trends over time. But honestly I found that less interesting than the prospect of seeing the spatial distribution of crime in DC.

1 comment:

  1. Have you checked your local PD web site? In Kansas City the PD links to a national data base that tracks crime by the type of crime. Put in your zip code and it gives block by block crimes. You can sort out by offense and the time period. You can check you block or the whole metro. Any thing in between. I used it a lot when I needed to move. Fun to tell apartment managers that all the crime they claim doesn't go on around their property is on line. ahmcguffin (again) Oh, in KC some of the stats get slewed by the Police asking people to go to the police station to fill out a report. the crime stat doesn't get logged as the address it happens at. Way to keep those nice neighborhoods nice.