We are featuring some old images today and tomorrow. First up: Hong Kong's material flows as depicted in a famous case urban metabolism case study dating back to 1978. Hong Kong has often featured in urban metabolism studies, because its unique characteristics of a city that is a densely populated, island-based economy allow for a higher degree of control and understanding of the physical movement of resources in and out of the city. This same study was replicated in 2001 and we have featured that graph earlier. As you can see, those graphs are very similar and the authors definitely did their best to conserve the original. In fact, as can be seen in this original graph our doubts about what that black spot above the skyline is has to be attributed to this original graph, where again it is not clear what this represents. A map outline would be our best bet at this point.

From the paper:

Diagrammatic representation of the flow of important materials into and through the settlement of Hong Kong. All units are in metric tonnes per day. Arrows are intended to give some indication of the direction of flow of materials.

(note how even this description is nearly the same in the 2001 publication!)