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 
Any issues with pics/cities, let me know.
A lot of them seem really odd size, like only taking up a tiny portion of the picture box. Makes it hard to see. For instance, Vienna, Kharkiv, Rotterdam, London, Dnipro, Birmingham (almost normal width but bottom seems to be cut off).
Those cities were fine for me, but I had that cutting-off-issue with other images. Also some images were very small. It looked like an internet issue, but it’s weird that it only happens with some pictures.
It seems like you only get to see what the previous city was if you actively skip it, if the 30s timer runs out the “Last City” field is unchanged