Race and ethnicity data by Washington DC police zones

If you've got arrest or incident data from the Metropolitan Police in Washington DC, and that data is broken out by police district or public service area, you may want to compare it with the racial and ethnic makeup of the people living in those zones.

If so, this post is for you.

The US Census doesn't break out populations by police districts. But in DC and other large cities, census blocks serve as atomic units that usually do fall within police precinct boundaries. So by knowing which blocks are within which districts, you can calculate the populations. Unfortunately, block-level data is only available from the decennial count, so the latest data is from 2010.

This is my third spin at such data — I've also done New York City and Chicago. 

In this zip file there are four data files:

dc_2010pop_by_2020police_districts.csv is the 2010 US Census data on race and ethnicity (just Hispanic or non-Hispanic, alas), summed by DC's seven police districts, as those boundaries are drawn today. The columns follow the Census bureau's coding: 

  •     P003001 - Total population
  •     P003002 - White alone
  •     P003003 - Black or African American alone
  •     P003004 - American Indian and Alaska Native alone
  •     P003005 - Asian alone
  •     P003006 - Native Hawaiian and Other Pacific Islander alone
  •     P003007 - Some Other Race alone
  •     P003008 - Two or More Races
  •     P005001 - Total population (again)
  •     P005002 - Not Hispanic or Latino
  •     P005003 - Not Hispanic or Latino: White alone
  •     P005004 - Not Hispanic or Latino: Black or African American alone
  •     P005005 - Not Hispanic or Latino: American Indian and Alaska Native alone
  •     P005006 - Not Hispanic or Latino: Asian alone
  •     P005007 - Not Hispanic or Latino: Native Hawaiian and Other Pacific Islander alone
  •     P005008 - Not Hispanic or Latino: Some Other Race alone
  •     P005009 - Not Hispanic or Latino: Two or More Races
  •     P005010 - Hispanic or Latino
  •     P005011 - Hispanic or Latino: White alone
  •     P005012 - Hispanic or Latino: Black or African American alone
  •     P005013 - Hispanic or Latino: American Indian and Alaska Native alone
  •     P005014 - Hispanic or Latino: Asian alone
  •     P005015 - Hispanic or Latino: Native Hawaiian and Other Pacific Islander alone
  •     P005016 - Hispanic or Latino: Some Other Race alone
  •     P005017 - Hispanic or Latino: Two or More Races

dc_2010pop_by_2020public_service_area.csv is the same thing, but aggregated by public service area — which are smaller units within a police district.

dc_2010blocks_2020policedistricts_population.csv lists every census block in DC along with its population data and both the police districts and public service area. The files above aggregating populations by police district and public service area are pivots of this file.

dc_2010blocks_2020policedistricts_key.csv is the "Rosetta Stone" of the project, linking block numbers (as "GEOID10") to police districts and public service areas. I did this using the QGIS open-source mapping software, with some batch processing and visual inspections of each zone.

Caveats

I'm pretty confident in the process here, but that doesn't mean I didn't make mistakes. You can check my math in the Jupyter notebooks I used. Generally DC police boundaries run along census blocks pretty closely. There were a few big blocks that straddled zones, but each of those was either in water, in a park, or, in on case, on federal property. So the residential population numbers should line up nicely.

That said, remember that this population data is 10 years old — and a lot has changed in DC in that time. For now, it's the best we have. We'll get new numbers with the 2020 census (fill out your form!)

Let me know

Tweet at me at @jkeefe if this helps you ... and especially if you find anything amiss. Also hit me up if you'd like this for data work you're doing in your city.