The object of this quiz is to adjust each circle’s radius so it contains the target population shown at the right. When you click Start you will be shown a marker on a random populated world grid square (there are over 800K 10×10 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 500 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 2.5 and 250 million people. Then click submit. You are scored on how close your circle’s population is to the target.