This is an interesting "Systems Diagram of a City", found at:

http://en.wikipedia.org/wiki/File:Systems_diagram_of_a_city.png

And the image appears on the wikipedia page for Emergy, and is labelled "Energy system diagram of a city in its support region"

http://en.wikipedia.org/wiki/Emergy

This diagrams the major energy  flows in and out of a city.