First choose a difficulty by typing ‘beg’, ‘int’, ‘adv, or ‘exp’ – Beginner is 200km radius, Intermediate 100km, Advanced 50km, and Expert 25km. Then, enter 1K+ population cities and all 1K+ population cities within that radius will automatically fill in.
hugequiz Premium members will see the 50 largest missed cities at the end of the quiz as large, purple markers.
NEW: Premium members can now also play a 3-hour time limit 'custom' coverage quiz of any distance from 5km to 500km, simply enter the distance followed by a '.' instead of choosing from one of the four levels, i.e. '350.' Quiz score is not recorded for the custom coverage option.
NOTE: the source citypopulation.de does not have a some Belarus/Russia/Ukraine smaller places such as villages so that data isn't available.
Quiz Takers 
I encountered a weird error – I typed in Spain and it brought up a list of what I presume to be the largest cities per letter per country, sorted by population. I typed in a bunch of cities it would “take” my answers but nothing was revealed and my score was [answers]/0. I kind of have an unbeatable score in Spain now though, lol.
Forgot to add – issue was gone on refresh. Probably just an issue with not loading the country – the country listed was on the side, but it was clearly pulling from all European countries.
hmm must be a one-off bug – i’ll remove that score.
For the Netherlands, you included a category which starts with an apostrophe (‘). The answer for that character is given as ‘s-Gravenzande, while ‘s-Hertogenbosch is the given answer for ‘S’. ‘s-Hertogenbosch is correctly written with an apostrophe though, and should be the answer for that category instead of ‘s-Gravenzande. Or you could remove the ‘-category entirely.
yeah I’ve fixed this – the apostrophe shouldn’t have been included as a letter.