[on the edge of something] close to the point at which something different, especially something bad, will happen:
1.Their economy is on the edge of collapse.
2.She is on the edge of despair.
[on the border of]:the official line that separates two countries, states, or areas, or the area close to this line:
1.a market town on the border of England and Wales
前者側重指程度，後者指方位。