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.
        
                    
             
        
        
        
Answer:
Even though we are apart, we are united!
Explanation:
I miss my family and friends, but I have to stay home unless I have an appointment. Please... stay home and stay safe everyone!
 
        
                    
             
        
        
        
<span>The United States was on the winning side of World War II.</span>