Digital artist and illustrator Chaotic Atmosphere from Geneva, Switzerland have made some really beautiful work, mapping the influence cities have on their surrounding environment using digital tools.
Map of Venice
The almost invisible fluid streams flow through tre streets and into the environment of some of the worlds biggest cities in this series of illustrations. They are made using digital citymaps - treated as 3D terrain and mixed with more terrain to make erosion flow.
Map of Tokyo
Map of Cairo
Map of New York
Map of Beijing
Map of Rio de Janeiro
Map of Paris
All illustrations (c): http://chaoticatmospheres.com/