Earlier this year, we wrote about the symbolism of October 31 in marking the day the world population reached 7 billion people. A design firm based in Boston, Mass., Fathom Information Design, created “Dencity,” a map of global population density as the world reaches this important milestone. The map uses different size and color circles to represent the distribution of population and density around the world. Larger and darker circles show areas with fewer people. Smaller and brighter circles represent more crowded areas.