In a city like London, the fact that cultures live together and cross-fertilize is a beautiful and natural thing. The many cultures in Amsterdam contribute to the city's high level of craziness - something which every interesting city should offer. But sometimes immigrants can live in parallel worlds which can exclude others and not be very attractive.

Another thing I like about German cities - and it's an advantage which they haven't sufficiently exploited yet - is that they are pioneers when it comes to environmental technologies. And green solutions are becoming more and more important.

Detroit is an urban hell. But even in this city of the dying auto industry, there is reason to hope, if they manage to combine the creative forces of designers and other intellectual "suppliers" in other ways.

As industries migrate toward the Far East, the future of many Western cities will no longer lie in manufacturing products but ideas and patents. Young, mobile elites can choose where they want to live, and they can easily move, which means that cities are involved in a heated competition for the best people. Only the most attractive cities can benefit from this development.

Some remain great cities, but they shouldn't stand still. They should move in the direction of a knowledge-oriented society. Most cities have to do something to draw attention to themselves and make their particular assets visible on the international radar. I'm not talking about developing countries, but about the United States and Europe.

I like what Barcelona is doing. This city almost perfectly combines its natural advantages with cultural attractions, IT parks and first-rate educational opportunities. The same applies for Dublin, which manages to achieve a blend of complexity, tolerance and artistry and makes a point of not devoting every part of the city to the tourism industry. Sometimes creativity also means forgoing short-term profits and simply saying no.

In a city like London, the fact that cultures live together and cross-fertilize is a beautiful and natural thing. The many cultures in Amsterdam contribute to the city's high level of craziness - something which every interesting city should offer. But sometimes immigrants can live in parallel worlds which can exclude others and not be very attractive.