What made peoples call America, Europe as western countries and Asia and alliance as eastern countries? Thats the importance of 'DATE LINE'. As we all known Asia's right edge and America's left edge will be close in globe but not in DATE, the time will totally be different. For example take a boat from Asia to America in a fine Saturday evening you'll reach America by Friday night of the same week! weird isn't it. Its not time travel anyway.
Since it is stated that Asia will receive the sunlight of a day first we are on the Eastern side, America receives the light late on same day so they are on Western side! Map has nothing to do with it but the 'Date line' has!