1. Are kilometres still used to measure really large distances?

Yes, even though you could use a unit such as a megametre, for say, the circumference of the Earth, it is usually given in km.


2. What units are perimeters measured in?

Because a perimeter is the measure of the distance around an object, it is a length, and its units would be mm, cm, m, km etc.


3. Who first decided how long a metre would be?

Originally the French decided a metre would be one ten millionth of the distance from the Equator to the North Pole.