San Francisco has many lovely qualities, but huge swaths of the city smell like pee.

@mattyglesias it's because it doesn't rain. The typical daily urine dose of most cities really accumulates. — Zach Beiley (@zbeiley) October 3, 2015

Some people think this has to do with a lack of rain, either in general or recently.

@mattyglesias one more cost of the drought identified — X to the M (@xaviermalina) October 3, 2015

But that doesn't make very much sense. California has been experiencing drought lately, but there are plenty of cities that are drier than San Francisco. My hypothesis is that other cities don't smell as much of urine because they don't have as many people peeing on the street.

I can't prove that's right, but I can come close, thanks to a fantastic animated map that a data visualization enthusiast who goes by simply "William"(found via David Curran) made showing reports of human poop on the streets of San Francisco. Building on Jen Wong's earlier work building static poop maps of the city, the map clearly shows two things: that there are a lot of people pooping on the streets of San Francisco (so much so that it sometimes shuts down BART escalators), and that the trend is toward more pooping recently.

I conjecture that street pooping and street peeing tend to be closely correlated and that in San Francisco's case the underlying cause is an epidemic of homelessness — am epidemic generated, in part, by overly restrictive zoning that prevents the construction of enough new homes to accommodate the number of people who want to live in the Bay Area.