First choose any Europe 10K+ pop city by entering it and choosing it in the drop-down box. Then, name any Europe 10K+ city in each 100 km circle/ring as the rings expand outward from your city of choice, trying to name SECOND LARGEST city in each circle. The first circle will include your city of choice as a possible answer.
PLEASE NOTE - You must type a '.' (period) after each city to submit it to prevent answering another city with a name you would be have to type to get your answer. If multiple cities have the name you submitted, only the largest one will be counted.
You accumulate points based on the population of the city you named in relation to the second largest city in the circle. A smaller city’s point total will be the ratio of its population to the largest, so if you name a city of 75K people and the largest city has 100K, you get 75 points. Naming the largest city will get you points based on the ratio of the 2nd largest city's population to the largest city's.
When you run out of time or end the quiz, you will see the current ring’s 2nd largest city at right (under ‘Answer Stats’ by your coordinates).
For example, if you choose ‘Paris’ – you will be shown a circle of radius 100 km centered at Paris. Naming any city in this circle (including Paris) will cause another ‘ring’ of radius 100 km to appear outside that circle, however - you will want to try naming the SECOND LARGEST city you can to get more points. After completing that circle, you now need to name any 10K+ Europe city in the new ring (but not within any previous circles/rings), again trying to name the 2nd largest city. If there are not two cities within the next ring of that distance, the ring will keep expanding by that distance until two cities fall within it.
Quiz Takers 
Fredensborg seems bugged
this is fixed – was under Fredensborg Stationsby.
Missing a lot of cities around copenhagen.
Ballerup, Herlev, Glostrup, Gladsaxe, Søborg, Rødovre, Hvidovre, Gentofte, Hellerup, Holte, Ishøj, Albertslund, Klampenborg, Vandløse, Skovlunde, Charlottenlund, Bagsværd, and so on. Hope to have them added in some way. Maybe a newer list of city names is available.
those are municipalities, Denmark uses urban areas as the closest thing to cities, or if they are in the Copenhagen area their census counts them toward Copenhagen total.
They are not all municipalities. E.g. Søborg is a town Gladsaxe municipality. I get that a lot get bunched in with Copenhagen as a greater urban area, but it’s waay too “inclusive” in this quiz. In general, most municipalities are named after the largest city in the area, but some have different names e.g. if they used to be two municipalities that were then joined and to make it “fair” they made a 3rd name, usually a nearby lake, forest, or something similar landmark’y.
yeah I just go by my source, http://citypopulation.de/en/denmark
That source identifies Copenhagen as ~ what is normally referred to as the “greater Copenhagen area”, but that’s a region not a city. Somewhat subjective too. It would probably be better to go by municipalities as the umbrella parameter, and then focus on the cities after that. But I get that the source doesn’t do that and you would have to do them manually so I understand completely. It’s just that the natives might be somewhat annoyed. E.g. in Copenhagen there is an enclave (Frederiksberg) that is it’s own municipality (and city) but for all intents and purposes have merged with Copenhagen, similar to the suburban areas.
CityPopulation lists Statistics Denmark as its source. So if anyone disagrees with what’s considered a “city” in this context, it’s probably best to raise it with Statistics Denmark (a Danish government agency) and their definitions/methodology.