World population density visualizer, by Derek Watkins, via Metafilter and gizmodo. The original idea goes back to William Bunge‘s “Continents and Islands of Mankind”, redrawn at Making Maps. There we have a map of the areas where population density is greater than 30 per square kilometer, roughly “where people live”; Watkins adds a slider so you can change that number “30” to anything from 5 to 500. Here’s a static map of the same data.
You should in theory be able to determine the population of the world from something like this, but the slider only goes up to 500, so you can’t tell how many people live at densities greater than 500 per square kilometer; these are “urban” densities (roughly) and so that’s a lot of people. Robert Talbert mentioned something similar on Twitter a few days ago: can you estimate the population of Colorado from a population density map? Not really, since the population of Colorado is very concentrated.