Desire paths

Philosophy — the ground remembers. A desire path is the line worn into a lawn between where the paving is and where people actually want to go. Planners call them cowpaths, or erosion, or vandalism; some universities now lay no paths at all for the first year and pave whatever the students wear in. What is interesting is not that people disobey — it is that nobody chose the shape. No walker here has a map, a memory, or an opinion about roads. Each one only wants to get from A to B and slightly prefers ground that is already easy. The network on screen is not a plan anyone had; it is the field's memory of everyone's journeys, and it is legible — you can read the traffic matrix off it, which pairs of towns matter, which junction is load-bearing. Paths make walkers, and walkers make paths: the causation runs both ways, which is exactly why the result is neither designed nor random. Move a town and watch the argument replay: the old roads do not get deleted, they get forgotten, and for a while the map holds both the city that was and the city that is.

Technique — positive feedback, saturation, decay. Three ingredients and there is no fourth. Feedback: walking a cell raises its comfort, and comfort attracts walkers. Saturation: wear is applied as +w × (1 − G), so ground already bare cannot get more bare — without this the busiest road would run away to infinity and every other route would be invisible beside it. Decay: comfort leaks away everywhere at a fixed rate, which is what makes a route have to keep earning its existence. The whole character of the thing lives in one number. The desired direction is the unit beeline to the goal plus comfort pull times the gradient of comfort, sampled through a blur — the blur is the walker's eyesight, the radius at which a track becomes visible as a track. At pull 0 the walkers are ideal commuters, every trip a straight line, and the field is just an X-ray of the traffic. Turn it up and the straight lines start bending toward each other, meeting, and merging: the network buys shared infrastructure by spending detour. Too far up and the detour is unlimited — everything collapses onto one superhighway that visits every town in turn, which is efficient for the ground and terrible for the walkers. The classic desire-path network, with its triangular shortcuts and its slightly-too-long gentle curves, is the narrow band in between, and it is a compromise nobody negotiated.

Aesthetics — wear as light. The obvious rendering is a dirt map: brown lines on green. It is honest and it is dead, because it shows you where the ground is damaged. This is dusk from a few hundred metres up instead, and wear is drawn as light laid down by use — the brighter the road, the more feet have passed. That is a claim, not a fact: nothing here glows, the glow is a colour ramp plus two blur passes. But it is the right claim, because a desire path really is an accumulation, the visible residue of thousands of small private decisions, and light is what accumulation looks like. The ground is kept nearly black and faintly mottled rather than flat, so that the faintest half-abandoned trace still has something to be faint against; the towns are given halos rather than icons, so they read as places with gravity rather than as nodes in a graph; and the walkers are small enough that you lose individuals and see flow. Watch a ghost road fade after you move a town — that slow dimming is the piece.