social networks are starting to fulfill some of the interactions upon which cities are traditionally based
Manchester - first formed as a settlement in 76 and 1301 there was a town charter and in 1700-1850 because of industrial revolution it grew ten-fold though not formally recognised as a city until 1853.
People who study urban growth talk about the role of technology (field rotation etc...) on the development of cities.
"I think the internet is going to have as profound effect on cities but we're only at the beginning."
See Richard Florida Flight of the Creative Class.
Jane Jacobs talks about the essence of cities, especially cites in which you can walk. In a car you are isolated but on foot you overhead conversations, have encounters and even change your behaviour based on those encounters. The characteristics of good cities: random encounters, information storage and exchange, communities, space to play, economies of scale, trade/sharing, organised complexity, anonymity.
Diversity drives innovation. We need to create more space to cross-fertilise our ideas.
Roland's just mentioned a really interesting idea of "bothies": random shelters that people can use for free?! See here for more info: http://www.mountainbothies.org.uk/