Biggest cities between each 10 degrees of longitude, with a map

Can you guess every country in Europe based on its flag?

With the help of a map, try to name the cities of the world with an urban area population of at least 3 million.

Can you name every city in the world whose urban area has more than one million people - with the help of a map?

In each randomized group, name any answer which matches the first category to reveal the second category, etc...