In this graph the urban metabolism of two cities is compared: the Greater Toronto Area (1999) and Hong Kong (1997).

From the paper: [this figure] shows a systems flow diagram comparing selected flows for the GTA [Greater Toronto Area] in 1999 and Hong Kong in 1997. This type of diagram is commonly used in materials flow analysis and can be used as a communication tool to convey information to policy-makers and the public.

This diagram does convey some basic information and it is easy to understand. It is good to see, however, that the visual appeal of data visualizations has improved over the years.