You have heard of the gold rush and railway mania of the 19th century,  not to mention the dotcom boom of the late 1990s. Observe now the  latest land grab - to build a three-dimensional replica of London,  complete with streets, shops, parks, even the underground system, on  
the internet. At least five companies are doing this and most of them  are unaware of all of their competitors.

The theory is seductive. Build a 3D London and you can rent out  apartments and shops, get advertising, boost heritage sites and  familiarise tourists with the capital before they arrive. And, of  course, go out clubbing and meeting people.