Population Duel
Which country has more people? There are two ways to play: an open-ended streak, two countries at a time, and a daily challenge where you rank 8 countries.
Free mode: two countries
Two countries appear with their flags and you tap the one with more people. If you're right, one of the two stays for the next round against a new country, and the streak goes on until your first mistake. So that no round is a coin toss, the bigger country in each pair always has at least 40% more people than the other. A timer runs during your streak: the mode's ranking goes to the longest streak, and ties go to whoever was faster. A streak of 15 unlocks the Census Champion achievement.
Daily challenge: rank 8
In the Daily Challenges you get 8 countries to sort from most to least populated. Press and hold a row and drag it into place. You submit once and there is no going back, so check the order before confirming. You win if at least 6 of the 8 countries end up in their exact position. Afterwards you see where each one really belonged. The challenge is the same for everyone, changes at midnight UTC and keeps its own streak.
Tips
Place the ends you're sure about first, the most and the least populated, and fit the rest in between. Size on the map is misleading: Bangladesh has more than 170 million people and the Philippines more than 110 million, while Mongolia and Kazakhstan together have fewer than 25 million. It also helps to remember that Nigeria now has more people than Russia, and Ethiopia more than Germany.
In the daily challenge you don't need a perfect order. If two countries are very close and you can't tell which goes first, make sure you get the rest right: 6 in place is already a win.
What you learn
A realistic sense of how big each country is in people, which has little to do with how much space it takes up on the map. The figures are recent UN estimates and are the same in the free mode and the daily challenge.