This is cool! I made a similar quiz a while ago. I think I made my range to large however with 100 km instead of fifty. It's kinda cool to see how the answers are different!
Amman (5.20 mil) is 37 km from Jordan's border (a well fortified - and mined - border, where we had to show both the Jordanian, then the Israeli, border guards our passports to get across!).
Well, you could consider OECD statistics that encompass the Belgian cities of Kortrijk and Tournai, for a total of 2.6 millions but it cannot be implemented in that quiz since it breaks an obvious rule, being a binational metro area.
Brussels centre (Ville de Bruxelles, Grand Place) is also 49 km from the Dutch border (Zeeuws Vlaanderen, near Koewacht). Just guessing the 2.025.000 population is below the cut off. :)
And by the way way, Bratislava is the current capital of Slovakia, but used to be the capital of Hungary, during Habsburg rule when it was called Pressburg.
Kuwait might be a stretch, but within reason Maputo to the Swaziland border would be 49 km :). The population also seems to make the 2.2 million cut off.
Cologne and Dusseldorf are two distinct cities that can hardly be called a common urban area. You might as well include Bonn, Duisburg, Leverkusen, Moenchengladbach, and Neuss as well.
Citypopulation.de takes "the Ruhr" and Cologne/Düsseldorf as it's two Urban / Metro Areas. Lots to argue about. Adding Ruhr in this one would be just as weird as any arbitrary other choice.
I enjoy the geography quizzes, but it seems it is getting difficult to find a topic that hasn't yet been covered. I worry that someday we will find ourselves being quizzed on such things as "major cities whose names were changed within the past century which are are situated within 100 miles of a capital city in another country whose name ends in ia and whose flag has no red on it."
it's probably the combined statistical area of nine counties around it (as used by US statistics sources), as even the urban area in 2010 was only 3.7m. That covers an area of about 75 miles across that is linked with the city.
I'm guessing all of South Holland is included in that statistic