While browsing through some of my older bookmarks I discovered this page of what seems to be an information portal of one of a German federal ministry. The Sankey diagram for cost flows they show reminded me of a feature in the Umberto material flow management software, which I always wanted to inspect in more detail.

Using their 30-day trial version I worked with one of the simple demo examples they provide. Basically this software is a modeling tool for process systems and analysis of material flows within any kind of process system (production plant, supply chain, region, …). Sankey diagrams in Umberto are not the default view for material flows, but one can switch from the normal “Material Flow Network” view to the Sankey view.

Even though the Sankey diagram feature of the software would need some retouching, I was surprised and extremely pleased to see a “Cost Sankey” feature.

You can enter material direct cost for all materials (in the ‘bucket factory’ example of the demo all materials already have a “market price” property), as well as fixed and variable process costs. The variable process costs are spread over the process throughput using ‘machine hours’ or ‘work hours’ as cost drivers (i.e. to link cost creation to the material throughput). Thus, at every process (shown with blue squares in the flow diagram) the costs -or should I say: the value – increases. Going from left to right along the general flow direction in the Sankey diagram you can see clearly that the growing magnitude of the Sankey cost flows… a kind of ‘Value Added Sankey diagram’.

The above screenshots show the overall cost for the three products produced in the bucket factory (Fig.1), the cost per unit for each of the three products of the bucket factory (Fig.2).

The following two cost flow Sankey diagrams are for the individual costing units ‘plastic bucket’ and ‘watering can’ (Fig.3 and 4). Please note that on theses diagrams a part of the machines is not being used, so they don’t add any process costs to the costing unit (or don’t contribute to the value added). Unfortunately you can only display either mass or energy flows in one Sankey diagram, so the energy costs (from the circle labeled ‘other materials’) are not shown as a Sankey flow, even though they add to the price for each product.

Last weekend I had the possibility to visit a friend in the Netherlands, and we took a tour of Rotterdam Port. Despite the bad weather, I was fascinated by the huge container ships, the cranes, the noises….

Back home I did some research and came up with the cargo data for the year 2005 from the Port of Rotterdam website.

I did the following three Sankey diagrams. The first shows the inbound cargo quantities (in million tons gross weight of cargo) from the left, and the outbound quantities to the right, broken down to world regions. One can clearly see that Rotterdam handles mainly imports, with more than 281 million tons of cargo being unloaded, while only 88,2 million tons of cargo are being loaded onto ships.

Next I flipped inbound and outbound flows to the same side. However, I think that by this the diagram loses somehow, also because some purple flows (outbound to Africa and Oceania) are too thin.

In the third version, I added a shape for the balance difference between inbound and outgoing goods.

Tell me what you think about theses Sankey diagrams. It would be interesting to compare Rotterdam to other ports. Shanghai, for example, might have the opposite picture with much more exports, but I haven’t found any data yet to show this. And, if we are talking cargo traffic: how about doing a passenger Sankey diagram for one of the international airports in the U.S. (by origin/destination continent?, by airline?)

A scan of one of the first – if not THE first ever – published Sankey diagrams has now been added to the Dutch and German Wikipedia articles. Actually I had always wanted to get hold of a digital version of this this energy efficiency diagram published by Captain Henry R. Sankey in 1898 in the Minutes of Proceedings of The Institution of Civil Engineers. Vol. CXXXIV, Session 1897-98. Part IV.

First Sankey diagram published 1898 in JIE (Source: Wiki Commons)

Click here to see the image in original size.

Sankey used this novel type of diagram to represent energy flows and energy losses in a steam engine, comparing it to an ideal steam engine.