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.
あ
つ
None
What's the first sound in Asia? It's A (あ). Nice and easy!