How to design a city?

I'm going to throw an idea into the mix and say that London is probably the perfect city already. That's because it hasn't been designed. It has grown up over a couple of thousand years organically, to suit the needs of Londoners.

this is wrong. the City of London has grown "organically". Most of the rest of london has been designed. Covent garden, Soho, Mayfair, Fitzrovia, etc not to get into the Victorian suburbs.

Sorry - being pedantic.