Living tightly packed requires a certain trust unique to cities. In my rural home town no unfamiliar faces pull in to get gas at the Citgo. No strange children show up to play ball at the North Lansing Firehall. With an average grade of less than 100 children, everyone in the Lansing public school system knows each other, has a cousin in the grade ahead and a sister two grades below. People become part of the town’s tapestry, have kids in the school musical, coach each other’s children in little league and hang out at the lake together in the heat of August.

Living near each other in Tokyo requires forgetting where one person ends and the next begins, sacrificing self for the ability to return home on the last Saikyo line train. Stepping out in Yonohommachi in 2002 I remember most the first block, back along the train tracks, still wrapped in scents that were not my own. Beer. Sweat. Food I had not eaten. Perfume I did not purchase, or apply. For several blocks, until the streets became small and the crowds disappeared, until I passed the grapevines, I was not entirely myself, having given up my scent to the city of Tokyo.

In so many ways living in a city requires vigilance. In Ithaca in 1997 I used to leave the keys on the floor of my 1984 Volvo 240, windows rolled down to the summer heat. In San Francisco in 2014 strange sounds wake me in the night and my first instinct is to check on our Volvo, a 1997 model now, parked on the street outside. Our apartment doors, often open in Houston in 2009, are secured carefully in San Francisco, watched over by cats and by neighbors. Yet it is that trust of neighbors that persists, that grows. Because unlike in Lansing where I played ball or built tree forts with our neighbors, here we know little of each other’s lives, but watch each other’s doorways anyway. Here we are brought to trust by proximity rather than through history. We have the loose friendships of the city, temporary and without concern for the unknown. One neighbor receives keys to our apartment for a week, and we hers, on the basis of a single shared fact: that we each own a lonely feline. There is no elaborate period of getting to know each other, no shared holidays or family stories, just need, ability, and trust.

These are the relationships unique to dense urban environments, and the faith in each other I think of each time I pass my wallet and transit pass down the length of a crowded 38 bus so that someone unseen can swipe it and, hopefully, return card, wallet, and contents to me. It is the trust I repay in swiping some unseen person’s card on the panel in front of me, all of us twisted by the bus’ lurching into a human pretzel of shared motion.