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 
Was asked a city in Saarland starting with the letter ‘K’. I wager there are none. Just two municipalities but they do not have town privileges.
Also Saarland only has 17 cities with town privileges so there are no cities on ranks 21-30 by population.
Also I had Karlsruhe for some other category but it was not counted as a gimme toward Pop 250-500K south of 49° Latitude, which clearly it is.
Köln doesn’t count toward NRW cities with 2-5 letters, which is inacceptable.
There is no city in Saarland with 2-5 letters, nor one starting with a G. Also Glatten is not a city but a municipality without town privilege. No cities in Saxony-Anhalt ending in U.
Cities on this quiz are all ‘settlements’ based on this site:
https://citypopulation.de/en/germany/
This quiz uses English spellings like all my other blackout quizzes for determining letter-based criteria.
Why does Hannover not count as a city with 8-9 letters for Lower Saxony?
it’s under the English spelling of Hanover.
I think this will become one of my favorite quizzes here. Anyway – something seems to be wrong with the Pop 250-500k category, mostly it shows empty fields (where there are actual cities that would fit…)
there are only 12 cities of 250-500K population in Germany, 8 of which are in North Rhine-Westphalia, so a number of states won’t have an answer for that column.