The Corner Shop.

I walked past a shop in Paris the other day that appeared to sell almost nothing but mustard.

Not mostly mustard. Not mustard alongside the olive oil, vinegar, biscuits and emergency tins of tomatoes. Mustard seemed to be the actual business plan.

A few streets later there was a cheese shop devoted, of course, entirely to cheese. All refrigerated and proper. A slaboratory of refrigerated ingots, in various shades of yellow.

Then one selling just brushes - brooms and dust-busters, with maplewood handles, all the way from somewhere. Another selling chocolates, handmade and self-important, and next to that, a butcher whose blood-red, oxygen-rich cuts looked like you could eat them raw.

None of this is particularly remarkable in Paris. Which, when you think about it, is a remarkable thing.

I have always understood how a little specialist shop often (but not always) survives in a village. Our decidedly well-run boulangerie has a fairly compelling commercial advantage in that if you want bread without getting into your car, the bread shop is where the bread is.

What I had never really considered was how the opposite works. How does the man selling only cheese survive in one of the busiest, most expensive cities in Europe? How does somebody look at the ground rents in Paris and conclude that the soundest commercial way ahead is shelves full of mustard?

The answer, it turns out, is because there are an awful lot of people outside.

Paris is the biggest city in France by a country mile, as well as the densest and most relentlessly metropolitan. Yet instead of specialist shops being squeezed out by the sheer size of the Capital, the city seems almost to breed them: butchers and bakers and shooting-stick makers; vendors and menders; purveyors of fenders. Whatever the single thing is, someone in Paris has built a shop that sells only that.

And the bread tells much of the story in one quietly civilised statistic: something like ninety-four percent of Parisians live within a five-minute walk of a boulangerie.

Not a shop. A bakery.

Fresh bread, daily, is treated by the largest city in the country almost as basic infrastructure, like drains or streetlights. The boulangerie du coin is not part of some Potemkin-esque arrangement of quaintness laid on to satisfy the insomniacal iPhones of Asia. It is where you go for your bread.

Which raised, as I wandered, munching, down the Rue du Bac to the Orsay Museum, an obvious question. How do they do that?

The romantic answer - and I like it, so I said it first - is simply that Parisians want it this way. They want the baker who knows them by name, the butcher who understands, the cheesemonger who knows that tasty freebies make sales.

There is a relationship there. A daily commercial theatre of belonging that no supermarket has ever quite managed to fake or make. The Parisian appears perfectly willing to visit four shops to accomplish what could technically be achieved in one. Which is a splendid values statement in an otherwise eye-wateringly expensive City.

But romance alone doesn't pay a Paris rent. And this is where the thing became more interesting to me, because I'd misunderstood the economics - which, for someone with a degree in economics, is troubling. I had always assumed enormous cities were hostile to tiny businesses. That is more or less what bid-rent theory predicts: the most expensive land goes to whoever can wring the most money from it, and the man selling only cheese cannot compete with a bank. But the theory only covers the supply of space. It says nothing about the demand pouring past the door. Density, it turns out, is the specialist's oxygen.

The man selling only cheese can sell only cheese precisely because, within a few minutes of his door, there are enough people who want very good cheese to keep him occupied for life. In a village, he'd probably starve. In Paris, he can afford to be particular. He could probably just sell Brie.

The city also performs another useful trick. Its numbers swell significantly during the working day. Commuters pour in, tourists arrive, offices fill, and suddenly the neighbourhood shop isn't just serving the people who live round the corner. It's selling to everyone who happens to pass its well-stocked window and discovers, at lunchtime, that they too fancy a decent ham sandwich.

The very scale I assumed would favour big grocery also creates enough customers to support the small grocer. Paris doesn't keep its little shops despite being enormous. It keeps them because it is enormous.

The supermarkets, of course, tried. They always try. And they're all here in Parisian mini: Monoprix, Franprix, Carrefour City and all the rest, dotted around the city doing useful things for those who shop there. But something curious has happened to them.

Denied the acres of car parks, enormous trolleys and the weekly big shop that allow supermarkets elsewhere to become aircraft hangars selling yoghurt, the Paris “supermarket” has had to shrink. And then shrink again, until eventually it begins selling sliced bread, a few decent cheeses, some wine, microwave dinners - the same things you could get from the specialist shops around the corner, only worse. The supermarket arrived to replace the specialist. Paris made it specialise instead.

The convenience store is a white flag.

But there is another reason these shops remain, and this one surprised me more.

Sheer willpower.

Because Paris doesn't merely hope the right shops survive. In certain parts of the city, when a commercial property comes up for sale, the city can effectively put its hand up and take first refusal. Through schemes originally run by a semi-public company called Semaest, and now Paris Commerces, it has used pre-emption rights to buy shop premises before they vanish into the ordinary churn of the property market. It renovates them, then puts them back into use with precisely the sort of neighbourhood business it wants there, at a rent the business has some hope of paying.

Consider that for a moment. A butcher does not have to outbid whatever trade can extract the greatest number of euros from a single square metre of Paris.

Sometimes Paris can simply choose the butcher. It's a little like playing SimCity with real people.

More recently, that thinking has fitted neatly into the city's much-discussed ville du quart d'heure - the idea that the ordinary necessities of life should exist within a fifteen-minute walk of home. Which means the five-minute baguette isn't entirely an accident of French good taste. It is also policy, and rather good policy at that.

There is something quietly moving in that. A city looked at its butcher, baker, cheesemonger and greengrocer and decided they weren't merely businesses. They were part of what made the place worth living in - that the heart of an arrondissement was a thing worth legislating for.

It isn't all roses and ribbons, and honesty is required here. Paris has lost almost half of its dedicated butcher shops in twenty years, with fewer than five hundred left as I type. Changing diets explain some of it; the price advantage enjoyed by supermarkets explains more. Paris is not immune to any of this, for all its efforts to hold back the convenience economy.

So protection isn't preservation. But it is a fighting chance, and the city is trying hard to keep these doors open - which still requires people to walk through them each day. They do, in numbers.

Every morning people leave their apartments with bikes, bags and baskets to perform the choreographed dance of shopping the quartier. It starts early. Fresh bread and salads, a piece of cheese here, a warm apple tart there. Something for lunch. Something for dinner. Nobody is going to take you aside and say “this is so efficient,” because it clearly is not. It takes longer. You have to walk, or find somewhere to leave the e-bike, and stand in line behind someone counting out exact change as though their life depended on it.

But maybe that's the point.

Because perhaps we shouldn't measure a city only by how quickly it lets us buy things. There ought to be room in the arithmetic for talking to your neighbours, leaving the car at home, and watching a dog stare thoughtfully into a butcher's window. The baker knows your bread. Somebody says bonjour. Somebody complains about the weather. It is a conversation with every purchase - which is not something a supermarket has ever managed, where the trolleys and the minutes both go by unnoticed.

Which brought me back to our own little bakery, in our own little village. Because our baker is doing well too - surviving, perhaps even thriving - but for almost exactly the opposite reason.

The Paris baker survives because thousands of people glide chicly past his door. Ours survives because there isn't another baker within ten miles. Paris sustains its boulangerie through abundance; our village sustains ours through scarcity. One has almost too many customers; the other has almost no competition.

And yet, by completely opposite routes, the great metropolis and the tiny French village arrive at precisely the same conclusion: fresh bread, five minutes away, from somebody who knows your name.

The Town Mouse and the Country Mouse, it turns out, eat exactly the same breakfast. They just built completely different worlds to get it.

Anyway, I never "close this essay with a poem", but I am going to choose to this time. This is from a lovely piece of verse by Jean Guthrie-Smith, called "Street Market". Have a read if you are sufficiently inspired...

"...Here are dainties both pickled and bottled,

And carcasses hung in the street,

And dreadful things clammy and mottled

Slabs, slices and bundles of meat.

Great Mackerel, spotted and spangled,

Grey codfish and horrible peeps

Of crab claws, and lobsters all tangled

With shellfish, in pyramid heaps.

All strange things that live in the deeps

Are here for your will at a penny,

All chilly and briny and blue;

For this is the mart of the many

And not the mart of the few..."

On Platform 13, wholeness isn’t found - it’s remembered. Because loss is loss, worthiness is universal, and no one is alone. We are all in this together.