Single-use paths through the city are produced in the following manner: a map of its streets, ideally eleven inches across by seventeen inches tall, is laid out on a level surface. Next, a single shell is loaded into the cartographic apparatus, filled with a mixture of cuttlefish ink, magnetic gel, and iron shavings. Finally, the trigger is pulled, allowing the electrically-charged cocktail to splatter across the entire breadth of the page.

The subsequent patterns show jagged paths through the city which can only be traversed once. The wanderer must be actively carrying the produced map for such shortcuts to be visible, and each disappears approximately one hour after the map was made (at which time its brittle ink begins to crumble). As such, anyone who intends to use such a path must do so quickly and decisively, and furthermore, if they have a specific destination in mind, they should be prepared to exhaust numerous maps and shells until an exact combination is found which leads them there.

Because the paths indicated by these maps cannot be retraced, it follows that only one person can ever actually use each one successfully. Anyone who attempts to accompany or tail the person using it will find themselves lost and separated somewhere along the way.

On the other hand, the carrier has a once-in-a-lifetime experience. There are entire neighborhoods, restaurants, and even shopping malls which only exist in these liminal spaces. Strangers who are met here are always happy to have company, for they rarely ever see anyone pass their way, and likely never will again. Their lives are bound to the conjunction of map and territory, and most do not live past the point at which the ink that birthed them fades.

Such matters are one of the major reasons why single-use paths remain unpopular; that, and the fact that following them is an experience that cannot be shared. Most who use these byways simply keep their heads down and ignore their surroundings until they arrive at their destination.

Magnetically-charged ink can have other consequences.

The ammunition for this apparatus can also be used for tattoos.

The lives of those born from ink can be short indeed.