After showing two variants for visualizing the U.S trade balance in my last post, I got aware of yet another option. The first figure (infographic by Spiegel Online) used the length of the arrows to express the value of imported and exported goods. My remake version used the magitude (width) of the arrows, as is typical for Sankey diagrams.

In this figure (by Anthony Cohen, University of Illinois, 2012 / Wikicommons) for US trade in 2011 the arrows for import (red) and export (green) are proportional to the total value of goods, just as we are used to see it in a Sankey diagram. But the arrows are superimposed, with the narrower green export arrow on top of the wider red import arrow. This creates another, somewhat more dramatic impression.

Data shown is for 2011 in billion USD for the 15 most important trade partners. Arrows are not labeled with absolute figures, instead a legend at the bottom indicates the width of five default arrows. The arrow from and to Mexico is a problem (no joke intended!), but the legend clarifies that arrows don’t indicate a specific geographic routing.

Another Figure from OECD/IEA World Energy Outlook 2014 report showing energy exports/imports from/to five African subregions.

Coal measured in million tonnes of oil equivalents (mtoe), oil itself shonw in millions of marrels per day (mb/d). Natural gas measured in “bcm” (anyone?).

Given the different units for the flows I think only arrows of the same color should be compared). So not really a Sankey diagram…

Drawing Sankey diagrams on a world map to show flows between different geographical location is always a challenge. One of the inherent problems is that large (=broad) arrows may run between two points on the map located very close to each other. Another problem is that one wishes to have the arrows more or less along the actual trade routes, which in many cases is close to impossible (take, for example, ships going through the Panama or the Suez canal).

I have shown quite a number of ‘Sankey diagram maps’ here on the blog, but most of them had shortcomings. Now here is an example that does extremely well in tackling the issue of Sankey diagram flows on a world map.

(CC licence – Carbon Brief)

This flow map of coal exports around the world shows the top exporters. It was crafted by Rosamund Pearce for the Carbon Brief article “Mapped: The global coal trade”. She decided to route the Sankey arrows nicely sorted, in parallel, and not along the actual shipping paths. See how much of the coal trade from Indonesia to China is led “virtually” south of Australia and New Zealand? Additionally the arrows are not led precisely to the actual port, but rather connect at a suitable place of each continent. With these simplifications the trade flow map is much clearer, understandable.

Another world coal flow diagram from 2012 can be found here.

South China Sea has recently garnered increased media attention due to China reclaiming land and building an airfield on Fiery Cross Reef. The territorial dispute regarding Spratly Islands has been simmering since the 1970ies when oil was discovered in the region. South China Sea is also “one of the busiest shipping lanes in the world” with “more than half of the world’s supertanker traffic, by tonnage, pass[ing] through the region’s waters every year” (Wikipedia).

The Department of Energy has two interesting maps on their beta website showing LNG and crude oil transport for 2011.

Transport of liquefied natual gas (LNG) in trillions of cubic feet in the South China Sea:

Transport of petroleum in millions of barrels per day in the South China Sea in 2011:

(both maps from website)

These are ‘Sankey-inspired maps’ rather than exact Sankey diagrams. Arrow widths are not maintained where the shipping routes pass through narrow straits. Nevertheless, transport volumes are generally on a correct scale.

Martin Grandjean digitized and vectorized Charles Joseph Minard’s World Map of Migration from 1862. His recent post reminds us that no too long ago migrants were also moving from Europe to other places of the world.

via – full vectorized image 2 MB here

The map, based on data for the year 1858, “shows migration flows that contrast with the maps of the twenty-first century. That year, 86.000 Englishmen left their country, as 45.300 Germans, 20.000 French and 11.600 Portuguese.”

Read this interesting post from the Cartographia blog for additional detail on the map.

From a technical point of view, the only criticism I have of Minard’s map is that the direction of the arrows is not indicated. It requires the reader to know about origins or destinations of migration.

You can see the original Minard migration map (“Carte figurative et approximative représentant pour l’année 1858 les émigrants du globe, les pays dóu ils partent et ceux oú ils arrivent”) in this 2009 post and at Wiki Commons or directly at the Library of Congress.

You might want to check out another related June 2015 article by Martin Grandjean, where he points out some shortcomings of migration maps.

The 2012 GEA Global Energy Assessment report (GEA Global Energy Assessment – Toward a Sustainable Future, Cambridge University Press, Cambridge UK and New York, NY, USA and the International Institute for Applied Systems Analysis, Laxenburg, Austria) features five maps showing energy trade in the world on pages 128/129.

These can almost be considered Sankey diagrams, so I am featuring them here on the blog.

This one is for embodied energy in trade goods.

And this one is a classic oil and oil product trade flows map:

Flows lead from a specific color-coded region to another. The quantities are clustered in arrows with three different widths as shown in the legend (1, 5, 10 Exajoule)

Blog reader Panalion sent me a photo taken in Amsterdam’s Botanical Garden. It is of a map showing coffee and tea flows from producing countries to mainly Europe and North America. Panalion writes “I thought you might like this Sankey map I found attached to a cable between two palm trees. There were chairs set up to accomodate school classes”.

This map is for didactic purposes and features no absolute figures and no year. In addition to the export flows of coffee and tea shown as arrows the map also has circles of three different sizes representing percentage of world production of coffee, tea and cocoa in the originating country.

Infographers might have better ways of showing this information. But in this case I think it is sufficient to get the message across to the target audience, the school kids.

Actually not a Sankey diagram, but a map with Internet sea cable bandwidth. Eight differently coloured widths each of the “bands” representing max capacities in gigabits. No oriented arrows obviously as packages travel in both directions.

via whiteafrican

Original SVG file is creative commons, access here.