Nextdoor works a lot like Facebook, but instead of a "Like" button, it offers a "Thank" button, encouraging a kind of neighborly grace. More important, in order to join, you have to prove that you live where you say you do (by entering a code mailed to your home address, for example). Which means the community you enter is not imagined or diasporic, comprising people from the same school, profession, or interest group—it's physical. You can "mute" neighbors on Nextdoor to hide their posts, but you can't make them move away. Like it or not, these are the people in your neighborhood—the people that you meet each day, as the old Sesame Street song goes. Not just the postman and the barber, but also the aspiring belly dancer, the night clipper, the cat looser, and all the rest.

Thanks to its popularity, the service offers a unique window into daily life around the country. Nextdoor's virtual communities—which cover more than 180,000 U.S. neighborhoods, including more than 90 percent of those in the 25 largest cities—are becoming representative of the country's actual populations.

What do Nextdoor users talk about? On April 18, 2018, to pick a random day, the nation mourned former First Lady Barbara Bush, Japanese Prime Minister Shinzo Abe visited Donald Trump to discuss North Korea, and the world reacted to a deadly accident aboard a Southwest Airlines flight. But on Nextdoor, the overwhelming majority of Americans were focused on the impacts of late-season snowstorms: stuck cars, downed power lines, and especially snowplows. Grout and kittens were on mountain-time minds, and Oregonians seemed to be enduring a spate of lost wallets and duck encounters. In Florida and Colorado, problems with telecom services dominated the conversation.

This is pretty normal. Steve Wymer, Nextdoor's vice president of policy, told me that the same topics arise again and again, modulated by region and neighborhood type. Service requests and recommendations constitute 30 percent of chatter, and discussions of real estate make up another 20 percent. About 10 percent of Nextdoor conversations relate to crime and safety, Wymer said. (Suspicious persons come up a lot, often amounting to sightings of people of color in predominantly white areas. Nextdoor has attempted to discourage posts that use appearance as a proxy for criminality by prompting users to add more detail and blocking some posts that mention race.) Public agencies such as police and emergency-management departments also post updates to their constituencies. Noise complaints are another popular subject, according to Wymer—fireworks seem to raise particular ire—as are classifieds, missing pets, and gardening tips.

Judging by the conversations on Nextdoor, it would seem that Americans are concerned first about the safety and security of their property, family, and pets, and then with their property's, family's, and pets' upkeep and improvement. Though the platform breeds its share of conflict, it is notable—in contrast to other social networks—for the commonality it reveals, even in these times of unprecedented political division. No one, Democrat or Republican, wants a neighborhood strewed with dog poop.