The answer would be "to help you decipher symbols and scale."
Without the key, a lot of the symbols would be quite confusing and you wouldn't know if it was 5 miles or 500 miles. Everything else is implied throughout the map, but the key's purpose is definitely to help you decipher symbols and scale.
B. by enticing the reader with exciting action
I think these are right
1. Budha
2. years
3. wanted
4. and
5. sign
6. traveled
7. One
8. ??
9. war, death
10. known
