Type 'easy' or 'hard' to begin the quiz. Easy is a 15-degree grid, hard is a 10-degree grid. Then, try to name the largest 50K+ cities in each square IN ORDER. To name a city, you must first click on the grid square to make it have a GREEN border. Then, type in the city answer for that square followed by a '.' (a period).
The squares will start with '0/5' (or maybe fewer cities if less exist in that square). Click on a square and enter the largest city in that square not yet answered (so, the largest city if you have yet to answer a city in that square). You will then have '1/5' and need to click on that square to name the 2nd largest city, and so on until you complete all the cities up to 5 (or less if less exist). If you name an incorrect city in a square it becomes 'locked' and turns red and you can no longer accumulate cities in that square.
You receive 1 point for the largest city in a square, 2 for the 2nd largest, and so on.
At the end of the quiz the largest remaining city you haven't named will be shown in each square.
Quiz Takers 
why is hanoi not counted in this quiz. it counts jeddah as bigger than hanoi?
Per citypopulation.de, Jeddah is slightly larger.
Tip: write down which countries you have completed once you get the message in the top right, then you won’t try lots of different cities in e.g. Mexico when you’ve already completed Mexico. That way it will be easier to get to the point where it shows the remaining countries.
The quiz is very laggy for me with the new visual effect where the lines slowly cover the screen.
Hmm, not seeing this at all, what browser you using? How is it laggy, just when the lines fill in?
I have the same problem, but i dont know if it is my wifi. I am using chrome and when I type the city the lines fill slowly and i cant type very well.
I use Edge. The quiz stays slow for me until the lines are completely filled out. Which means that the quiz is usually laggy from beginning to end.