First choose the number of cities by typing ‘100’, ‘250’, '500', '1k' or 'all' – then try to achieve the highest population among the largest English cities (min 500 population) you chose. Quiz is not timed.
hugequiz Premium users have the option to choose any number of cities to play the quiz with (stats are processed but score isn't saved). Simply enter #(number of cities)# to play the quiz with any number of cities from 25 to the maximum. For example, to play the 300 largest cities, type #300# to begin the quiz and you will play it with the 300 largest cities. Entering #all# will play it with all cities - all cities will also be chosen for any number chosen above the total.
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.