The wedding of Prince William and Kate Middleton will be a huge media event. The TV audience is likely to be 2 billion, and 12,000 journalists will cover the ceremony.

What most spectators are interested in, of course, is the romance and the pageantry. But as someone who was in charge of the marketing of London for eight years, including during its successful bid to secure the 2012 Olympic Games, I can't help looking at it from a more professional angle - as an economic opportunity for marketing and branding a city and a country. As a growing number of China's cities are taking marketing themselves increasingly seriously, it is an event worth studying in that light.

Naturally this is not because China can mechanically copy London and the UK, nor does it have to have royal weddings for success! Some pieces of China's marketing are already superb - Zhang Yimou's opening ceremony of the Olympic Games, for example, had a global impact.

But the UK, and London in particular, does have a particular expertise in "destination marketing," which is worth studying. London is the world's most internationally visited city. It was successful in the contest to stage the 2012 Olympic Games against extremely tough competition from New York, Madrid, Moscow and Paris. That the UK will stage a wedding that certainly will be the most watched in history shows a similar skill. It is therefore worth looking at the significance of what might be termed the "wedding economy."

The first benefit, and actually not the most important, is the short-term one from the event. Spending by tourists and journalists who come will be measured in hundreds of millions of dollars. The rent of a single small pre-fabricated temporary TV studio to cover the one-day ceremony, not to speak of the much more extensive facilities required by major networks, is $100,000.

But even more important is the role of such a major event in long-term brand building.

It is a fundamental mistake in marketing to start off with a particular tactic or initiative. Good marketing cannot be made by putting together a number of unconnected events. The starting point must always be the brand and how any event fits with the brand. This applies just as much to a city or country as to any commercial product.

A key part of London's "brand" is that it is very old - the city was founded 2,000 years ago. London has been the capital of England considerably longer than Beijing has been the capital of China. Figures of worldwide significance, Shakespeare or Dickens, for example, worked there. The Royal Wedding fits perfectly with reinforcing the old. The 1,000-year history of churches on the wedding site, the cavalry, the fact that it is the Royal family burnish that image.

The question for London is how to combine in its brand the old and the new - and to show that the old is a resource for the new. A tourist may well come to visit a thousand-year-old site. A start up IT or biotech company will not benefit because of it.

For that reason London needs to find ways in its marketing to push new elements into this old image. For example, its promotional film to win the Olympic Games featured children (who are above all "the new") from Africa, Latin American, Russia and China - the key "emerging" markets. Doubtless those preparing the ceremony are working on ways to mix new and old – the sight of trees being transported into the church beforehand helps burnish green credentials, for example.

All such aspects are well worth studying by China's cities. Marketing a destination or a city is not particular adverts or tactical events. It is a question of working out clearly a brand image and then how individual events reinforce this over a prolonged period - and ensuring that each detail fits with this.

For most people the Royal Wedding will be a pleasurable moment. But it is also an extremely serious piece of marketing. The fact that its audience will be in the billions itself shows it comes from one of the countries that is still the best in the world in this type of marketing

In China most people will simply enjoy. But marketing professionals for China's provinces and cities might also find it useful to take notes.

John Ross is currently Visiting Professor at Antai College of Economics and Management, Shanghai Jiao Tong University. He was consultant to Fortune Global 500 companies and from 2000 to 2008 London's Director (currently equivalent to Deputy Mayor) for economic and business policy. He has written on China's economy for 20 years.