The growing population of the world, now estimated to be over 7 billion, marks a global milestone and presents obvious challenges for the planet.Â There are extremely densely populated cities and sparsely populated countries.Â China is the most populous country with India following closely behind. This post brings together some disparate illustrations of our world as it grows, including scenes from Mong Kok district in Hong Kong, which has the highest population density in the world, with 130,000 per one square kilometer. In Mongolia, the world's least densely populated country,Â 2.7 million people are spread across an area three times the size of France.Â Then there's Out Skerries, a tiny outcropping of rocks off the east coast of Scotland where the population is just 65.Â And doing what he can to contribute to that 7 billion global milestone is Ziona, the head of a religious sect called "Chana." Â He has 39 wives, 94 children, and 33 grandchildren. The world is an interesting place. -- Paula NelsonÂ ( 41 photos total