New visualization technique to map population density, by Fathom at http://fathom.info/dencity/ The map also highlights the 20 most populous cities in the world today.
“Dencity maps population density using circles of various size and hue. Larger, darker circles show areas with fewer people, while smaller, brighter circles highlight crowded cities. Representing denser areas with smaller circles results in additional geographic detail where there are more people, while sparsely populated areas are more vaguely defined.”
This map was created in response to the new milestone our planet has reached in being the home to more than 7 billion people. This map shows it’s not about absolute quantity, it’s about density. Not only are the dots smaller and closer together in the more densely populated parts of the world, but they are also brighter, which intuitively makes us think of these highly populated areas as glowing and vibrant. Perhaps this represents a little bit of unintended editorializing through visualization (or "visualitorializing," to coin a new word) on Fathom's part, or maybe even subliminal message-making, but these high-density areas DO tend to be the incubators of innovation and invention. In a bit of a twist on typical cartographic convention, such as in proportional symbol maps, the smaller dots signify MORE of the quantity being mapped.
“China. The largest city in the world is Beijing, with 17.8 million people. China is home to six of the twenty most populous cities in the world, more than any other country.” 
Gridded Population Density Map by CIESIN from: http://sedac.ciesin.columbia.edu/gpw/maps/globaldens.pdf
Gridded Population Density Map by CIESIN from: http://sedac.ciesin.columbia.edu/gpw/maps/globaldens.pdfOur friends and colleagues at CIESIN (Columbia University’s Center for International Earth Science Information Network) wonder if this Dencity map is an improvement over their own gridded population map, and whether or not it is showing anything new. Although ostensibly they are both mapping the same population density data (more-or-less: the CIESIN map is based on Year 2000 data and the Fathom map is based on more current population data), I would say that the Fathom map, first of all, is more gorgeous, and second of all, probably does a better job of highlighting the bursts of population density, and making it much more obvious where population density is most intense. It gives a better overall snapshot of population density at-a-glance, although it's very likely that the CIESIN method produces a more accurate and "scientific" map. See CIESIN's data and methodology at http://sedac.ciesin.columbia.edu/gpw/
Of course, grid-based cartograms are another way of depicting population density (as reviewed on a recent blog posting at http://geographer-notes.blogspot.com/2011/10/map-of-week-10-17-2011-gridded.html) 
WorldMapper's Grid-Based World Population Cartogram (2000), focusing on sub-national level data, from the ESRI website at http://www.esri.com/news/arcuser/0110/cartograms.html Thanks, Kristen Grady, for sending me the link to the Dencity “Infographic of the Day” at http://www.fastcodesign.com/1665513/infographic-of-the-day-a-strange-brilliant-map-of-the-worlds-population Check out other innovative Fathom visualizations at http://fathom.info/
Of course, grid-based cartograms are another way of depicting population density (as reviewed on a recent blog posting at http://geographer-notes.blogspot.com/2011/10/map-of-week-10-17-2011-gridded.html)
