How these maps were made

The simplest way of describing these proportional maps, or cartograms, is to think of them as a hybrid between a map and a pie chart.

In both cases the cartogram and the pie chart display nations in proportion to their carbon emissions. The only difference is that the proportional maps use country outlines as their starting point.

This means that international boundaries will almost inevitabley change shape as the data on climate change is added into the animation.

The next step is to give each part of the globe a particular value, to help fix it on the map. These values are then equalised to fit in with data surrounding a particular topic, in this case carbon emissions.

As the data is equalised the borders of countries contract or expand in relation to their production of carbon emissions, either per person or as a nation as a whole.

Drawbacks

Although these maps can help us visualise data they do suffer from some drawbacks.

For example, countries with a large land mass and a relatively small population, like Australia will often seem to shrink when the thematic data changes the shape of the world.

This large geographical starting point can mask the relative influence of countries such as Australia, which has some of the largest carbon emissions per person.

The opposite can also be true. When the map is viewed on a per capita basis, small countries with small populations, but high emissions per person, can grow extremely large as they change to fill their part of the proportional map. Luxembourg and the Gulf States are good examples of this.

To help limit this problem all countries with a population of less than 100,000 and land mass of less than 100,000 hectares have been left out.

More details...

The maps were produced by John Pritchard, from the Geography Department of Sheffield University, with help from Mark Newman at Michigan University.

The data on carbon emissions was sourced from the United States Department of Energy, 2004.

For more detailed information on how the maps are produced follow this link.