Hey there, not to sound pedantic, but citypopulation.de ranks Munich as bigger than Stuttgart in all but urban agglomeration, but the numbers there don't match with the quiz. Could you maybe be more specific in what page you got the data from?
I think a lot of Germans are confused, because we learn in school that the biggest cities in Germany are Berlin, Cologne, Munich and Hamburg. So, "Urban Areas" would be more accurate to put into the title of the quiz. Because now Frankfurt only counts because two other big, but totally independent cities (Wiesbaden and Darmstadt) are counted in. This would be never called Frankfurt, but "Rhein-Main-Gebiet".
Same with Cologne, on its own it barely cracks one million. To get to 5 million you have to stretch it far and wide and include cities like Düsseldorf, which would rather go to war then be included in "greater Cologne".
I'm sorry but I don't think the numbers add up. For Amsterdam, 2.4M is the number of people within the metro region, not even the urban area, which has under 2M. And Hamburg (which actually has 2.48 an not 2.88M in its urban area) is a bigger city than Munich but has a smaller urban area than Munich (2.60M). I'm not completely sure I'm right, but I think something got mixed up here.
Otherwise a nice quiz! Thanks!