Why does a map need a scale of miles?

Maps need a scale because they show you how far apart the distances are that you are reading. If you were reading a map of the United States, without a scale... someone (who probably doesn't know what the United States are) might think that the US is only 55 feet across.

Another example: say you were reading a map of Florida. The map happens to show Orlando, Tallahasse, and Tampa. Say you live in Georgia... and you're taking a trip into Florida. Once you land in Tallahasse, you want to drive from there to Orlando, then to Tampa, where you fly back home. Well, this map doesn't have a scale; that's a problem! You don't know how far Tallahasse is away from Orlando, or from Orlando to Tampa!!!! It's all just there to help you read the map. A map without a compass rose on it... well, you wouldn't know which way was north. Hope this helped!