The object of this quiz is to adjust each circle's radius so it contains the target population shown at the right but ONLY within Europe. When you click Start you will be shown a marker on a random populated Europe grid square (there are over 90K 10x10 km grid squares used for the data, courtesy of https://human-settlement.emergency.copernicus.eu/index.php). Also you will see an adjustable circle of radius 100 km to start. Adjust the circle's radius by dragging it until it contains the target number of people shown - this target will be between 5 and 100 million people. Then click submit. You are scored on how close your circle's population is to the target.
PLEASE NOTE: ALL of Turkey is included in counting population (not just European portion), and the portion of Russia west of 61.5 degrees E (just east of Chelyabinsk). Nothing outside Europe (such as Africa or middle east other than Turkey) is included toward the population count within a circle.
Quiz Takers 
With the recent number of cities, it is impossible to get a high score on the beginner level (9899 cities vs 9901 cities previously).
Yes it is constantly being updated as city-population.de updates – so soon it should be back above 9899.
When you’re back on the site, it’s currently impossible to get a high score, because the top scorers have 9468 cities and only 9462 are currently available.
I’m almost sure the previous version of the quiz (and the longitude one too) had a countries remaining counter which failed to be included in these updated versions. I think that counter is more or less a giving on coverage quizzes. It’s especially useful on higher levels where gaps are very small and I don’t have a clue on what countries I’m still missing. I think a 5/10 remaining countries would be enough.
Ah, the counter is there (though it reads States rather than Countries), but once we choose the level it’s gone so it’s all a matter of tweaking the quiz.