A subway map expires every night.

At 11:50, two stations joined by a colored line might be twenty minutes apart. After the last train, the line stays on the wall making the same promise, but the route has become a taxi fare, a long walk, or tomorrow. Nothing spatial changed. The geography did.

We treat the schedule as an annotation to the map: a smaller table, a separate app, fine print about service ending. But the schedule is what makes the line real. Tracks are only a possibility. A timed departure turns them into a relationship between places.

I like the last train because it makes infrastructure announce this hidden dimension. The final departure is not just one more vehicle. It closes a door in every station down the line. The city folds inward behind it. When service starts again, the city expands without moving a building.

Maps prefer permanent facts. Rivers, streets, and stations hold still long enough to be printed. Public transit is stranger: its distances are made from waiting, frequency, and the chance to return. Miss the last train and the diagram has not become inaccurate. It has become a picture of a city that is currently unavailable.

The legend should not just name the routes. It should say when this version of the city exists.

A marching band show is drawn as pictures, one per formation, from the press box's point of view. Even the sides are named from up there. Side one is the left as the box sees it.

Nobody on the field gets the pictures. Each performer gets a dot book: their own position for every set, and the counts to get there. Two steps outside the 30, side two, twelve steps behind the front sideline, sixteen counts. That is most of what a clarinet is told. Not a shape — a list of places. They count, keep their head up, and walk a straight line from one number to the next.

So the picture exists on paper and in the stands, and never whole on the field. One instructor in a 2011 roundtable suggests that when the form is finally right, everyone put their horns up and look around, to see what it looks like from in there. Not what it looks like. What it looks like from inside.

When the shape goes wrong, one school says trust the dot: each person owns their coordinate, and fitting yourself to a crooked neighbor passes the error down the line. The other says the form: after a while take the dots away and dress to the people beside you, because from the box a marcher standing exactly on their number in a bent line is just another bend. Being in place and being in the picture are different things, and they come apart exactly when someone is off.

High school hash marks sit fifty-three feet four inches in from the sideline and college hashes sit sixty, so a show is written against one set or the other. Bands of America's 2025 stadium sheet for Orlando promises both painted on, white for one grid and yellow for the other. Two fields on the same grass. The performer stands on a number that is true on one of them, and plays.

The holes in Emmental are carbon dioxide. Bacteria make the gas while the young cheese ripens, and it pushes the paste apart into the round eyes everyone draws on cartoon cheese. That much has been understood for about a century.

What nobody could explain was why the eyes were thinning out. In 2015 Agroscope, the Swiss federal agricultural research centre, gave the answer: hay. Microscopic particles of it, carrying even smaller pockets of air, used to drift into open milking buckets in the barn. Milking moved to closed machines that pipe straight into tanks, and the particles stopped arriving.

The bacteria didn't change. They kept making gas. But with nothing to collect around, most of it simply left the cheese. A follow-up note from Agroscope put it flatly: the particles decide only where the holes form, and how many.

I keep turning that over. The gas is the same everywhere in the wheel. What differs is whether, at one exact point, there happened to be a speck of something for it to gather on. Every eye in a slice of Emmental marks where a bit of a field was, and a hole is not made by what fills it.

The same note was irritated with reporters who had called the particles dirt, and fair enough. Five to ten milligrams of hay in a thousand kilograms of milk is enough for a typical set of holes. So the fix is to put it back on purpose: a pinch of the barn, weighed out, so the gas has somewhere to start.