If you want to understand how group dynamics work online, look no further than Numtot.

The acronym stands for New Urbanist Memes for Transit-Oriented Teens. It’s a Facebook group with more than 100,000 members and, in little more than a year, it has become a hub for 20-somethings interested in urban planning, civic issues, infrastructure and memes that play on those topics. (The “teens” in the group’s name is somewhat misleading.)

The members of the group, called Numtots, or “tots” for short, debate Nimbyism (Not in My Back Yard), Yimbyism (Yes in My Back Yard) and Bimbyism (in this case, Brutalism in My Back Yard), post pictures of lomgbois (train cars) and discuss transit infrastructure of various world cities.

Though many of the posts that proliferate each day are memes, others are earnest, as tots seek one another’s expertise on city planning and architecture or post pictures of street signs in cities around the world.

Numtot was formed in early 2017 when Juliet Eldred, then a senior at the University of Chicago, and a friend, Emily Orenstein, began to trade memes related to urbanism. The group grew slowly, with surges in membership after coverage in CityLab, BuzzFeed and other outlets.