Sorry to say you'll discover that much of it is attributed to humans.
San Francisco is a weird magnet for poop. Travel around the city in the grimmest of Easter Egg hunts, and you'll find turds basking on sidewalks, chilling in flower gardens, gumming up subway escalators—hell, you'll even find them littering the roof of a three-story building with no roof access.
I assumed upon moving here this was the marking of irresponsible dog owners. I wish I could still believe that. But Jennifer Wong has torn the brown veil asunder with "(Human) Wasteland," a revolting map of all the anthropogenic excrement around San Francisco.
Wong's venture into crappy cartography began with her needing a hack-week project for her company, HotPads. So the San Francisco native scoured the web for "cool" data sets, and found that the Department of Public Works, for whatever reason, keeps records of sidewalk cleanings for reason of "human waste or urine."
"Honestly, the data inspired me," she emails.
Unfortunately, Wong was shortchanged on several years of poop records. "DataSF's site said that they have information from 2008, but when I started processing it, I found that I only had six months' worth," she says. But it was enough to craft a map of the fecal landscape for part of 2013, shaded in the disgusting hues of an unflushed toilet. You can view the poo sightings as squishy piles (June 2013 is shown above), or as this heat map distressingly akin to an earthy stain:
Locals won't be surprised that the densest cluster of dung lies in the notoriously filthy Tenderloin. A healthy trickle descends into Mission, too, and smaller spots defile Chinatown and western Haight-Ashbury. If you want to know the situation on your specific block, enter an address into the map's search feature and it will attempt to answer the question: "Will I Step in Human Poop?"
As to the big mystery—how the city distinguishes human from beast leavings—Wong says she can't be sure. "I think that animals' urine and feces have pretty distinctive smells, so maybe that's the way you can determine on the fly," she guesses. Perhaps there's a professional scat-identification service involved?
(Fans of happy endings should know that Wong did, in fact, win grand prize in her office's hack week.)
H/t The Bold Italic