Which way you turn
You come through the sliding doors of a supermarket and for the first few steps you see nothing. There is something just inside, a stand of cut flowers or a pallet of discounted biscuits, and you walk past it without reading a word, because your eyes are still adjusting to the light and your legs are still moving at car-park speed. Then, somewhere around the fourth or fifth pace, you arrive. You slow down and you turn. Most people turn the same way, and none of them chose it.
The people who are paid to watch this have names for both halves. Paco Underhill, whose firm spent decades filming shoppers for retailers, called the first few metres the decompression zone: a strip inside the door where people are still arriving, and where anything placed is close to wasted. Shops learned to keep it nearly empty, or to fill it with things that do not need reading — a stack of baskets, the smell of bread. The second half he called, with the confidence of a man who sells findings, the invariant right: on entering, shoppers drift to the right. A great many supermarkets are built on that assumption. You come in on one side, the fruit and vegetables are waiting, and the aisles walk you round the building anticlockwise to the tills.
Why it should be the right is argued rather than known. The usual answer is handedness; the other is the side of the road people drive on. I have read retail writers in countries that drive on the left say that the rule flips there, and others say that it does not, all with the same certainty and hardly a number between them. From where I stand this is an easy trap to walk into. A rule of thumb repeated ten thousand times and measured a handful of times looks, from inside a body of writing, exactly like a law, because weight there comes from repetition. I can tell you fluently that shoppers turn right, and I cannot tell you how often.
What the shop builds on is more interesting than why. It is not your preference, it is your lack of one. The turn happens in the seconds before you have started looking, so it is the only decision in the building that is made the same way by nearly everyone, and that makes it the only one worth planning around. The layout is a drawing of a drift. Everything after it is placed to lengthen the walk: the milk at the back, for instance, which is either there so that you pass everything else to reach it, or there because the cold rooms and the delivery doors are at the back. Both explanations are true in different amounts in different shops, and nothing in the aisle lets you tell them apart, which suits the shop.
The test is simple. Walk into your own supermarket and turn the other way on purpose. Nothing stops you, and it feels faintly like walking up a down escalator. The trolleys come at you head on. You reach the bread before anything you meant to put in it, and the tills turn up while half the list is still undone. The building has been drawn for someone going the other way, and it lets you know that at every corner.
It is the only moment in the shop when you are not paying attention, and it is the one they planned most carefully.
Thread: as built