Technology companies have for years demonstrated the economic multiplier effect of increasing numbers of users in a given network: the larger the number of users, the greater the benefit to individual users. Facebook and other social networks are prime examples.
Cities have similarly been the centers of economic and intellectual development throughout history because they bring together people, resources, and ideas which leverage each other to create more economic value than is possible in smaller, more isolated areas. Young people leave the farm and go to the city for a reason: better jobs and greater opportunity.
Thomas Sowell's Wealth, Poverty and Politics builds on extensive international empirical research to demonstrate his thesis that it is the confluence of many factors including geography, demography, and knowledge (their network effect) which drives increasing prosperity while isolation and other forms of separation frequently result in lower prosperity or poverty.
Sowell's work does not bode well for the economic futures of Brexiteers and other nationalist political movements.