IMAGINE THE VIEW, around dusk, from the camera of a low-orbit satellite moving above a densely settled part of the world, and how this perspective allows us to watch a web of glowing cities, each flat, and etched as finely as circuitry, turn toward us with the silent inevitability of the planet itself.

Such a view reminds me of the life any of us might make in one of those cities, and of the ordinary hour in which we might walk home, say, after a meal with a friend, and stop for some bread and milk, and then, when we turn the key and set down our groceries and switch on a lamp, we fail again, as we almost always must, to imagine the illumination of which we form part, between the lifeless rock beneath the city and the airless void above.

Horizontally, too, a relative darkness surrounds every city, one composed of much smaller settlements, farms, and wilderness—all the regions that, at night, and from above, appear dimmer, if not entirely black. I like to think about the roads that run through these lands, and the signs that stand along them, signs that bear the city’s name, but which late at night may go unread for hours, and are perhaps not even lit until the headlights of a car sweep over them.

Each river has a watershed, the territory throughout which rain and melted snow descend to it; and similarly, each city has a region composed of all the hinterlands and provinces in which it’s signposted. Watersheds are illustrated most clearly on topographic maps, which suggest how we might envision a city’s name-shed, too: we could mark on a map every sign that points to a metropolis, and then connect these in a series of rough halos. Rippling out like contour lines, these would chart the field of the city’s gravity, and reveal the direction in which a traveler through the region would most naturally find themselves drawn.