In New York I had to narrow myself down to one out of a huge range of possible subjects. To some extent this was also true of my other destinations where considerations of time and space had forced me to focus on what seemed most significant or characteristic.

Here, I had to limit myself still more radically: New York is far too varied and complex a city to be reduced to a single common denominator. It's a Noah's Ark, a meeting place for the whole planet. Even on my first visit several years ago, I was struck by the impossibility of forming an overview.

After some hesitation, I decided to concentrate on the world of advertising. It is particularly important to the life of New York and is certainly more important here than elsewhere. But I could just as well have chosen other aspects.

I could have tried to show the city as a Tower of Babel with more Italians than Rome, more Jews than Israel, more Irish than Dublin, more Africans than many African capitals and almost as many Puerto Ricans as in the whole of that island. There are neighbourhoods which are primarily Chinese, German, Spanish, Greek, French, Arab, Polish-not forgetting the headquarters of the United Nations with its delegations, experts and journalists from every corner of the world

I could have photographed the third generation of skyscrapers which has shot up since the end of the War, creating astonishing glass and metal scenery. Each of these towers represents the equivalent of a small town: in the Pan Am building alone-which straddles Grand Central Station and is integrally connected with it-40,000 people come to work every day.

I could have told the story of New York with photographs of Central Park, which occupies some 150 blocks and functions as the lungs of the city. During the day, groups of musicians practise there, trendy young blacks show off their latest outfits, families picnic on the rough boulders, bathe in the reservoirs in the summer or try cross-country skiing in the winter. Baseball enthusiasts, dog-owners and chess players meet, each on their traditional patch, lovers clasp one another on the grass, white, black and yellow children fraternise on the massive sculptures of Alice in Wonderland characters, anglers are positioned around the lakes and squirrels come to pick food off the hands of old ladies. After nightfall everything changes: the park is plunged into darkness and becomes a lawless place where even cops hesitate to get out of their cars.

I could have illustrated the two worlds of Broadway, on and off, where theatre, musicals and dance are currently more vibrant than in any other capital.

I could have done a reportage on the art and antiques market. Apparently more than one twentieth of the world's treasures is to be found in the 120 blocks between Fifth Avenue, 42nd Street, Lexington Avenue and 86th Street.

I could have shown the different faces of Broadway, the avenue which snakes across the chessboard of Manhattan. Every time it runs into the square junctions of New York's grid, it generates the bizarre-looking buildings which give the road its character. Broadway begins down by Wall Street, runs through the slums of Lower Manhattan, winds through the maze of Greenwich Village, skirts past Macy's, widens at the height of 42nd Street under the bright lights of show-biz and the neon ads of Times Square, edges past the formerly disreputable districts of the West Side, cuts through the middle of Harlem, opens into Columbia University and ends in the miserable upper reaches of the Bronx.

I could have explored the boroughs neglected by tourists: Brooklyn, which is twice as populous as Manhattan, Queens which is 10 times larger, the Bronx which is 100 times poorer or Richmond where you might think you're in the country.

I had once considered stationing myself up on Rockefeller Center with a powerful telephoto lens to capture what was happening in the streets and on the rooftops, or even to peek through the windows of apartments and offices. I would have started at dawn and stayed till nightfall, returning in winter when the city is paralysed by snow storms, and in summer when the scorching heat triggers power failures: the network gets overloaded by all the air conditioning, and then people are left trapped inside elevators and failing lights create traffic mayhem at junctions.

I could have told the story of the ten thousand windows of the Pan Am building. Departmental heads are entitled to an office with just one window, Vice-Presidents of corporations get two, the Chairman and CEO get three (or even four if their companies are very important) and the big boss of Pan Am gets a whole apartment on the top floor. Humble employees work in the open plan interior under strip lights, dreaming of the promotion which will give them the right to a window-or else resigned to the thought that they will never get one.

But I chose Madison Avenue, the artery whose name has become synonymous with advertising. It's not as wide or majestic as Park or Fifth, and there are not actually enough buildings to accommodate all the agencies and their off-shoots: J.Walter Thompson, the oldest, and McCann-Erickson, Coca-Cola's agency, have moved to Lexington, Young & Rubicam has transferred to the Time-Life building on Sixth. The youngest and most dynamic agencies, Dane, Doyle, Bernbach (Volkswagen) and Papert, Kœnig, Lois (Renault) are on Fifth. Only BBD&O, Dupont de Nemours' agency, stayed on Madison. In fact, the world of advertising occupies a rectangle covering some 100 blocks, bounded by Third Avenue and 42nd Street, Sixth Avenue and 60th Street.

Within this area, you can easily distinguish who's who in the advertising bestiary. The most showy are of course the models who are distinctive for their long legs, the dark glasses behind which they hide their heavy make-up, the portfolios which they carry under their arms and their anxious way of rushing from one meeting to the next. In the '50s, most of them came from Texas, from Mississippi, or California. Now the advertisers prefer foreigners imported from England, Sweden and Denmark, and to a lesser extent Germany, Italy and France. Asians are beginning to make an appearance, but Africans are still not accepted except for advertising aimed at blacks. Some models specialise in haute couture, others in sportswear, swimwear, lingerie, teen fashions, senior or overweight styles. Still others are sought-after only for their hands, legs, teeth, hair or eyes. All of them are signed up with agencies, of which the best-known is Ford's, which represents more than 100.

The file they carry under their arm contains their best shots and is called the book. They hurry to meetings called go-sees ("go and see"). When they secure a job, they are paid 60 dollars an hour or double the rate for evenings and weekends. Some are rich and famous. The rest share bedsits with two or three other girls and regularly provide material for the suicide chronicles of the gutter press.

There are also male models, child models, baby models, animal models. All have their agencies, their books and their rates. The best paid are the animals, which is understandable: an advertiser who spends thousands of dollars on a TV commercial won't scruple to spend a few dollars more to ensure that the white peacock planned in the script is well-behaved and perfectly groomed. The most successful of the animal agencies is Lorraine Dessin, who keeps a menagerie of peacocks, lamas, monkeys, pumas, roe deer etc in her Greenwich Village apartment.

Less distinctive but much more numerous than the models are members of related trades: commercial artists, photographers, TV directors, "voices" for radio ads, stylists, TV advertising presenters, script-men, slogans-men, maquette-makers, market research specialists, inventors of advertising gadgets etc. Each carries his own portfolio and trots from go-see to go-see, and all of them live their lives alternating between highs and lows, between the dream of a penthouse in town or a weekend home on Long Island, and the fear of failing and being forgotten.

Success almost always comes through specialisation. You become a commercial artist known for plugging children's socks, or "the voice" of cheese commercials. Anyone who finds such a niche is keen to hang onto it: the amount of money spent on campaigns is so vast that advertisers prefer to avoid risks and only employ specialists with a proven track record. Thus ever more well-paid jobs are assigned to specialists drawn from an ever tighter circle who end up being stifled by excessive organization and stereotyping.

The kings of this universe are the art directors. They are recognisable from their impeccable suits, meant to impress financiers with their seriousness; but these outfits are always set off by some bohemian detail like a straw boater or a rose in the lapel to reassure these self-same financiers that the wearers are also innovators and creatives (the two magic words on Madison Avenue).

The art director enjoys a high salary and a secure job. He considers himself above the illustrators, photographers, film-makers, models etc whom he hires and supervises-as his job title indicates. The careers of these freelances depend on his goodwill, and they are all prepared to wait humbly in line to show him their portfolios. It is curious that the best paid of these "artists" are not necessarily held in high esteem: when referring to actors and models of every category (including babies and animals), advertising men use a generic term which originally had positive connotations, but which has ended up carrying a hint of disdain. That term is "talent". If the blonde in front of the camera doesn't praise her deodorant with enough fervour, the art director -who prefers to express himself through an underling-will say to one of his assistants: "tell the talent to give it a bit more feeling."

Art directors answer to account executives, the link men between agency and client (a "creative" is not deemed capable of communicating directly with a "commercial"). But the glory of successful campaigns-or the ignominy of failure-belongs to the art directors. This does little for their psychological equilibrium, and so they are famously the best clients of psychotherapists and the favourite targets of New Yorker cartoons.

I managed to take a few photos in the offices of McCann-Erickson, which occupies some 10 floors on Lexington Avenue and devises Coca-Cola's advertising campaigns in the countries known here as The Free World. (The use of this geo-political term is significant: total sales of Coca-Cola Inc. correspond with the highs and lows of American foreign policy; right now they're rising in Germany and India, but falling in France, Pakistan and certain Arab countries.) In order to co-ordinate its global strategy, McCann-Erickson relies on its own corps of ambassadors, some of whom are fixed and some roving, whose network runs as smoothly as the CIA or the State Department.

I followed the work of the committee entrusted with updating the International Pattern Book. This is a collection of "made in USA" advertising images, which McCann-Erickson puts at the disposal of Coca-Cola's concessionaries, to suggest advertising themes which might be developed in their respective territories, all the while adapting them to local customs and mindsets. In some countries of the Far East, for instance, red is the colour of mourning -so the colour of the famous logo had to be changed to blue.

To begin with, the Pattern Book committee examines the reports and suggestions sent from its various "embassies" and integrates them into an overall strategy. Then, on the basis of its recommendations, McCann-Erickson's art directors hire illustrators, photographers and film-makers to prepare visuals which the committee then discusses and selects, before submitting them to the highest authority, the board of directors of Coca-Cola Inc. But even before they are put to the committee, all these projects are scientifically tested using a procedure exclusive to McCann-Erickson. It consists of formulas elaborated by agency psychologists to select a sample of people whose ethnic and sociological profile corresponds with the target consumers. At the same time, the agency uses an apparatus of its own invention, meant to measure and record the variations in the iris of those tested: these variations appear to correspond with the degree of interest aroused by the image, and thus allow for a coefficient of effectiveness to be assigned to each ad, providing an accurate measurement of the relationship between future investment and commercial result.

The Pattern Book is the outcome of this work. It is printed in colour with very high quality resolution and distributed to all concessionaries. But none of these projects will actually be used for advertisements: Coca-Cola Inc. wants every concessionary to get them reinterpreted by local artists, so they will be best adapted to local conditions.

I was allowed to attend and to photograph a committee meeting. The topic for discussion was loaded with implication: the management had decided to base all its campaigns for the year to come on still life images showing Coke as a table drink placed amongst different appetising foods. But this raised numerous problems: could meat be shown in India? Are spaghetti popular in Northern Europe? What types of bread and cheese are appropriate for Belgium? The only project about which the committee was unanimous was an image which did not show any food, only a gigantic blow-up of the famous liquid spilling out of a bottle and sparkling as it was arrested mid-flow by the flash. The 12 experts seated around the oval table were favourably impressed. But a discordant voice piped up from behind. "It's excellent," said the young man who had got up to address the gathering, "but you might think the Coke was being poured into the gutter." The remark met with silence. Finally the Vice-President of McCann-Erickson, who was chairing the meeting, answered with a counter-question. "Is your objection founded on research or are you just expressing a personal hypothesis?"

It may be too easy to poke fun at these immense machines which try to be creative and which often end up being much less efficient than a small team or even a single individual with real talent. But the point of such machines is to reduce the margin for error: Coca-Cola's global success, like that of Detroit cars or Hollywood films, shows that the system is effective in consistently producing and selling goods of medium quality which answer the needs of average consumers.

But sometimes the system goes wrong. An error which may be minimal to start off with is compounded at every turn. As the machine is very well thought out, and safety margins have been set for each stage, the error may multiply for a long time before proving fatal, like in the case of those sick children who, despite some appalling infirmity, are allowed to grow up thanks to medical advances. A classic fiasco, which the guys of Madison Avenue still relive in their nightmares, was that of the Ford Edsel, a big car which was launched with a gigantic advertising campaign and which ended in historic failure. Yet Ford had overlooked neither tests nor market research. In fact, the checks were so scrupulous and exhaustive, and so many improvements were made that five years elapsed between the first model being designed and the product being put on the market: it was precisely in this interval that public taste changed, switching to cars which were smaller and easier to handle.

In order to avoid repeating such errors, Madison Avenue hires ever greater numbers of experts and artists, who are more and more specialised and better paid. Products and advertising campaigns are subject to yet more complex tests to reduce further the risk of error. But should error still creep in despite these precautions, the consequences would be even more catastrophic. This would not be so bad if it only affected Ford or Coca-Cola. But it might introduce misgivings about the efficacy of the whole system and erode faith in megaproduction and megamarketing.