Question

What is the purpose of a map’s key?

to tell what part of the world it shows
to show the directions
to give demographic information
to help you decipher symbols and scale

Answer 1

I believe it is D. to help you decipher symbols and scales.

Answer 2

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.