A question often asked about Worldmapper is in regard to our choice of colours for the different regions and countries. On the website we briefly explain that the colours used on the maps group the territories into 12 geographical regions, and allow for an easier visual comparison between the maps than would otherwise be possible. The shading of each territory within a region is consistent throughout all of the maps.” But there is a little bit more to the colours which tell a story about the unequal fortunes of the world which follow a general pattern along the major regions.
The colours of the world’s regions are chosen very consciously, and have a deeper sense behind their distribution. We split the world into twelve contiguous geographical regions of population groups, with every region being roughly symmetrically balanced and having at least a population of one hundred million people. This is how the world’s population is distributed:
We then applied a unique colour hue to each of the regions and applied different shadings of the colours to the countries (or territories, as they are, because not all territories that we use are independent countries) within that region. Each territory therefore has a unique colour that stays consistent throughout all worldmapper maps and helps to find your way around in the most distorted maps. The colour hues are also included in the supplementary material (such as the spreadsheets with the underlying data that we provide as a download along each map).
The actual choice of which colour hue goes to which of the twelve regions of the world was made by looking at the Human Development Report (we worked with the 2004 version at the time we developed worldmapper, the latest report and further information can be obtained from the UNDP website at http://hdr.undp.org/en/). We used the HDR to sort these regions from the poorest to the richtest. We then applied a rainbow colour scale to determine the colour hue for each of the regions, starting with shades of dark red to demarcate the poorest territories, then moving through the rainbow scale to a shade violet for the best-off region which is Japan. Here you can see, how the land area map relates to the colour scale of a rainbow:
But even without knowing that background, the colour scheme is a sensible design decision. It helps the map reader to identify individual countries and at the same time not get lost in the overall picture. One just needs to get used to the colours scheme once and is then able to read even the most distorted maps, such as this disturbing picture of executed death penalties:
The colour scheme has proven very useful so that I continued using it in the initial launch of the World Population Atlas. It was the first published series of maps based on the new gridded cartogram technique and (while it was also related to the Worldmapper project and therefore the colour choice seemed obvious) the colours helped to relate to our existing mapping approach so that the very unusual new shapes of the gridded cartograms appeared less intimidating to many of the visitors to our website:
Gridded cartograms, however, are much more complex than the original Worldmapper cartograms. Using just one colour in these maps makes very little use of its capabilities as a real map projection. This is a gridded population cartogram of the United Kingdom as I created it for the World Population Atlas. It is compared to a population density map to illustrate the differences between a choropleth display population density and a gridded population cartogram:
The choropleth map basically wasted its space for the choropleth overlay to display the information it wants to show. The gridded population cartogram in contrast gives equal space to the quantities that are shown in different shades in the reference map: It is an equal-population projection where every person in the UK gets an equal amount of space on the map. The geographical reference is retained at an objective unit, which is the grid. By displaying the grid and its distortion, the individual grid cell (each representing the same ‘real’ space in the physical world), the extent of the distortion helps to read and understand the geographic pattern and to comprehend the reference to the real world. Each grid cells retains its topology, and neigbouring spaces in the real world remain neighbouring spaces in the map. That is why this cartogram can be used like any other map: To draw other things on top of it – such as mountains, valleys and rivers (but also many other things – anything that has a spatial reference in the ‘real’ world that surrounds us). It is a map projection for the human spaces that surround us. Helps to read the world from our perspective – and therefore sometimes is even more powerful when seen without the familiar Worldmapper rainbow:
Now show this on a choropleth population density map…cartograms are not the better map, but they can sometimes be much more useful depending on what wants to be shown, just as is the case with any other choice of map projection…
Copyright note for the LandScan population data: UT BATTELLE, LLC. Developed under Prime Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The U.S. Government has certain rights herein.