Asia, Sub-
The kanji and the radical that look like this are exactly the same. They are both Asia. This can also mean sub-. As in subtropics, subspecies, subhuman… That kind of sub-! When it's not in a place name, 亜 will usually be using its sub- meaning.
亜 is associated with Asia because of its あ reading, but sometimes you might see it used as ateji for other place names as well. And don't forget that sub- meaning!
あ
つ
None
What's the first sound in Asia? It's A (あ). Nice and easy!
A is for Asia!