I am currently working in a research project about regional urban systems in Brazil.
It's all about urban networks: urban functions and urban hierarchy; Christaller; spatial distribution of cities and how they connect to each other; Sassem; management centers; Growth Poles, Perroux etc.
And when it comes to network of cities, it's hard to find good visualization at the appropriate scale. So I post here some really extraordinary visualizations presented by BBC (series Britain From Above)
Telephone Network
The Lights of Britain
Air Traffic
