How Many People Live in the Cities You Studied?

7 Billion: How Did We Get So Big So Fast?

http://www.npr.org/2011/10/31/141816460/visualizing-how-a-population-grows-to-7-billion

What is a Drip into the Glass?
What is a Drip out of the Glass?
Where are most people found today?  Was it the same 1000 years ago?
When did we reach 1 Billion people on Planet Earth?
What happened to slow the leaks out of the glass?
How long did it take to go from 1 Billion people to 7 Billion?
What are the issues we face to see if we can survive having so many people?

https://easyscienceforkids.com/all-about-top-10-largest-cities-in-the-world/