So I was trying to get as much people as I could with only 1 city (turned One City Challenge on). Starting as maya, walking north to build my city at the best spot. After a while my research was too low to research any techs (took 20+ turns to research a tech), so I decided to turn the slider to 0% en buy all the techs I would need. Since I used all my extra population as merchants, the money per turn was very high. Wait, why did you turn all your extra population into merchants? Well, a Great Merchant not only gives a gold bonus, but also +1 food. In total I got about 14 of them (+14 food = +7 pop).
Figured out nobody was going to trade me corporation/medicine so I decided to research it myself, but failed at getting sushi. I bought the techs up the refrigeration line and researched refrigeration myself. I was able to get Cereal's which gave me another +7/+8 food.
I reached 200M population in 2004. In 2020, Stalin had won a Time Victory, when there were almost 240M people in my city. In 2034 I reached the 50 pop number
In the 2070's America started eating my BFC tiles, even though my culture was much higher in the tile (about 79%), and they suddenly declared war on me. At this moment I gave up. It became too boring and my people were starving; I ended with pop number 52, which represents almost 310M population.
Note that this game was just for fun, and there is a lot of improvement left. E.g. I adopted pacificm asap for the 100% GP points bonus, but forgot to get a state religion. And most probably I could get even more food from Sushi instead of Cereal.
The biggest growths came from:
1) Opera House, which unlocked unlimited happiness
2) National Park, at this point I didn't need to get as much health resources as possible, as the unhealthy from population was removed
3) Biology, because every farm will get +1 food
Again this game was just for fun. If someone succeeds in getting 1B pop, you are a very good player. If someone gets 1B pop before 2020, you are a hero




Please forgive me if my English is not that good
