People are dying and being born every second of the day. You can watch where everything happens on this website.
Brad Lyon is a mathematician who created this map because he wanted to let people know what is happening in the world and because he wanted to make the numbers visual. He says that the U.S. population will go up by 44 percent in 2050. He uses various countries' Census reports as his primary source material.
What's most interesting is that population change is actually happening and his site really shows exactly when everything is happening. Most of the action is happening in India, China, and Russia because they are they are massive countries.