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Saturday, April 6, 2013

Screen Shots, Part II: Flow Diagrams

Flow diagrams, also known as Sankey diagrams, are a great way to see where a resource goes.  Starting from the left (usually), the diagram shows the sources of the flow.  Proceeding to the right, there is a column which contains the destinations of the flows.  This column might be the source of flows for another column, and so on.  The flows themselves are typically drawn such that the width represents the amount flowing from a source to a destination.

Sankey diagrams are a powerful visualization for seeing the big picture - the relative impacts of various things, bottlenecks, and dependencies.  Creating a Sankey diagram helps you to understand where everything is going.  If you are missing some data, the flows won't add up.  This is usually not a problem if your data all comes from one source.  In the case of several of the Sankey diagrams in Footprint USA, such as the Energy diagram, the data comes from a variety of sources.

Here is the national-level energy flow diagram from Footprint USA:

One of the most striking observations from the diagram above is how much energy is wasted - that's everything that is grey on the right side of this diagram.  But that is a topic for another post...

Footprint USA allows you to generate these diagrams for every state and county in the US.  You can also compare two regions.  Note the difference in the sources used to generate energy in New York state versus Washington state:

So, if you are driving and electric car in Washington state, it is primarily hydroelectric powered, while in New York you electric car is partially nuclear powered (Ford was ahead of its time).

Many of the Sankey diagrams in Footprint USA are interactive.  For example, you can tap on any of the boxes in the Transportation diagram, shown below, to display only the flows into and out of that particular box.

Footprint USA visualizes the flows of many of the major systems of our society, including Atmospheric  gasses, food, commodity flow, waste, and water use.

To see a wide variety of Sankey Diagrams, check out this site.  Lawrence Livermore National Lab has a site where you can explore deeper into energy flow in the US.

Watch for part III, Tree Maps.

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