Sankey diagram

Sankey diagrams are a specific type of flow diagram, in which the width of the arrows is shown proportionally to the flow quantity.

Sankey diagram which represents all the primary energy flows in to factory. The widths of the bands are directly proportional to energy production, utilization and losses. The primary energy sources are gas, electricity and coal/oil and represent energy inputs at the left hand side of the Sankey diagram . They can also visualize the energy accounts, material flow accounts on a regional or national level, and also the breakdown of cost of item or services.

Sankey diagrams put a visual emphasis on the major transfers or flows within a system. They are helpful in locating dominant contributions to an overall flow. Often, Sankey diagrams show conserved quantities within defined system boundaries.

Sankey diagrams are named after Irish Captain Matthew Henry Phineas Riall Sankey, who used this type of diagram in 1898 in a classic figure (see panel on right) showing the energy efficiency of a steam engine. While the first charts in black and white were merely used to display one type of flow (e.g. steam), using colors for different types of flows has added more degrees of freedom to Sankey diagrams.

One of the most famous Sankey diagrams is Charles Minard's Map of Napoleon's Russian Campaign of 1812. It is a flow map, overlaying a Sankey diagram onto a geographical map. It was created in 1869, so it actually predates Sankey's 'first' Sankey diagram of 1898.

The United States Energy Information Administration (EIA) produces numerous Sankey diagrams annually in the Annual Energy Report which illustrate the production and consumption of various forms of energy. The report for year 2012 include the following diagrams:

Eurostat, the Statistical Office of the European Union, has developed an interactive Sankey web tool to visualise energy data by means of flow diagrams. The tool allows you to build and customise your own diagram by playing with different options (country, year, fuel, level of detail, etc.).

The International Energy Agency (IEA) created an interactive Sankey web application that details the flow of energy for the entire earth. Users can select specific countries, points of time back to 1973, and modify the arrangement of various flows within the Sankey diagram.

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