Why is there an International Date Line?

Question

Why is there an International Date Line?

Answer 1

Things have to start SOMEWHERE, even on a globe/circle. It's where all the time zones start/finish.

Answer 2

The concept of an International Dateline is first alluded to by the 14th Century Talmudic commentary - Baal Hameor(Rabbeinu Zecharya Halevi) where he seems to indicate that the day changes at an area where the time is six hours later than Jerusalem (90 degrees east of Jerusalem - a line running thru China). This line which he refers to as the K'tzai Hamizrach (the easternmost line) is used to calculate the day of Rosh Hashana