Earlier quoted context omitted.
Geography nitpick: The airport in Istanbul is actually east of the Bosporus, making it Asia.
Hey mseebach, We had a few issues in the beginning defining these border countries and decided to allow Istanbul as Europe, but will definitely group it for Asia in future. We had a handful of difficult decisions, but luckily the winning entry visited all continents without contention. Guam was the tough one for us. Would you say Oceania?
Istanbul Atatürk (TAV) airport is Europe, Sabiha Gökçen (SAW) is in Asia. The border is the straight of Bosporus.
Continents are a rather vague concept[1]. Any definition is going to be arbitrary. For the purposes of your contest, I think the spirit would be to have gone to the continents "proper", i.e. I wouldn't count Guam at all, but say the continents are the mainlands of: NA, SA, Africa, Europe, Asia, Australia, Antarctica. I'd be inclined to allow New Zealand as part of Australia as the only exception.