Sharing NYC Police Precinct Data

Note: This post was originally published April 29, 2011. I've updated it completely with fresh info. Also just did the same type of calculation for Chicago.

Anyone doing population analysis by NYC police precinct might find this post helpful. 

Back in 2011, I wanted to compare the racial and ethnic breakdown of low-level marijuana arrests — reported by police precinct — with that of the general population. The population data, of course, is available from the US Census, but police precincts don't follow any nice, relatively large census boundary like a census tract. Instead, they generally follow streets and shorelines. Fortunately, census blocks (which in New York, are often just city blocks) also follow streets. But there are almost 40,000 census blocks in the city.

So I used precinct maps from the city and US Census block maps to figure out which blocks are in which precincts. With that, the population data is just math.

The original stories, and the Google Fusion Tables where the data lived, are all gone to digital internet history. But I've recreated them here, and also updated the calculations — some precinct boundaries changed slightly, and those on Staten Island changed significantly with the addition of a fourth precinct on the island in 2013.

So here are the updated tables. The population data is from the 2010 census, the precincts are as they exist as I write this in June 2020.

Have at it.

2010pop_2020precincts.csv is the 2010 population breakdown within each precinct as they are drawn in June 2020. The column headings are cryptic, but follow the codes starting on this page, which is from this rather large Census Bureau PDF.  

• precinct_block_key_2020.csv is the Rosetta Stone for this project. It has two columns: each block's identifier, which the census calls "geoid10," and the precinct in which that block sits. Note that some blocks aren't in any precinct, usually because they're actually in the water. 

• nyc_2010censusblocks_2020policeprecincts.csv contains base-level 2010 Census data for each block, married to the precinct for that block. For descriptions of the population columns, follow the codes starting on this page or see pages 6-21 in the Census Bureau PDF

• NYC_Police_Precincts_2020.zip is the official police precinct map shapefile, downloaded from the city's open data portal.

Caveats

I did my best to be accurate in computing the intersection of blocks and precincts, even generating precinct maps and inspecting them visually. But errors may exist. You can check my math in the Jupyter notebooks I used.

Census blocks generally fall nicely within precinct outlines, but they don't always. In particular, three blocks significantly straddle two precincts. If you're doing very precise analysis, you'll want to account for them:

• Block 360470071002003: An area near the north end of the Gowanus Canal in Brooklyn. About half is in Precinct 76 and half in Precinct78. Total people: 51

• Block 360050096002000: Mainly industrial. Half in Precinct 76, half in Precinct 78. Total people: 5.

• Block 360610265003001: This block consists of five similar-sized apartment buildings near the George Washington Bridge. The northern set of buildings are in the 34th Precinct, with part of one building in the 33rd. I put the entire block, and the 687 people living there, in the 34th Precinct. Looks like roughly an 80/20 split.

Credits

I originally did this work while at WNYC, using PostgreSQLPostGIS and QGIS. I was helped by the generosity and insights of Jeff Larson, Al Shaw, and Jonathan Soma.

If you find this information useful, drop me a note or post a comment below. I'd love to know about it.