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 
I’m sure there’s a valid reason for this, but why is Dorridge not counted as a valid place for this quiz?
It’s counted as part of the Knowle built-up area..I’ll add Dorridge as an alternate answer.
I’ve seen Vale come up as a top 3 city in South West England recently and St. Andrew in 4th-10th for south of 52 degrees. I’m pretty sure these are errors.
Otherwise, great quiz!
So if it says like ‘4th-10th largest in region’ and the square is ‘South of 52 Latitude’ that doesn’t mean the 4th-10th largest South of 52 Latitude – it means a city that is 4th-10th largest in the region where the city is (such as Vale is top 3 in Guernsey), and ALSO South of 52 Latitude – that’s maybe where you are thinking it is incorrect? The data is looking correct on my side – just maybe how you were interpreting the quiz.
Dudley came up as an answer for north of 55 degrees on one I took (unless there’s more than one!)
there is more than one 🙂
10+ Letters, Northern Ireland. You need to have Londonderry. The town is known as Derry by the Catholics and Londonderry by the Protestants, so “Londonderry” needs to be an acceptable answer for 10+ letters in the UK. The town is often cited as Derry/Londonderry for this very reason. They’re both official names of the city.
For cities with multiple names I can only have one main answer, so it’s Derry for this quiz. There are a number of cities like this in other countries as well.