Every time you describe something, you need to have a reference point. If someone says something is small, you might think, “How small?” A coin is small in my hand, because I am much bigger than the coin, but a coin is big enough to squish an ant. When we are talking about locations, like the earth, we also need reference points. If you wanted to meet your friend in the mountains where there aren’t any street addresses, you might tell them to meet you 100 steps away from the big round rock that looks like a lizard’s mouth. The rock is your reference point.

The North and South Poles are natural reference points for the earth. You can imagine the earth like a basketball, spinning between your fingers, as the earth does when it rotates around the sun. One finger might be the South Pole; it’s called the “rotation axis”, which is just one point where the earth spins. The direct opposite side of that finger would be like the North Pole. Another good reference point is the equator. This is the half-way point between the two poles, making a circle around the earth. You could stretch a rubber band around your spinning basketball and have it the same distance between your two fingers. The last point of reference for the earth is called the Prime Meridian. Almost 150 years ago, many countries voted on a certain line to be the Prime Meridian. For your spinning basketball, you would stretch another rubber band, but this time have it make a cross with the other rubber band.

When you have all four reference points (North Pole, South Pole, Equator, Prime Meridian), you can tell anyone where you want to meet them without needing an address. You just tell them how close you are to each of those points, and they can come find you.

The North and South Poles are used because they are easy for everyone to agree upon as reference points. It's where the earth rotates (just like the basketball example used above.) But you could use anything you wanted to! It’s almost like a code. You and your friend could always use a big round rock that looks like a lizard’s mouth as one of your reference points. Then you could tell each other how far away from that rock you are when you want to meet up. But if someone else wanted to use a different reference point, it might get confusing: they might not be using the same code as you. So it’s much easier for everyone to agree on the same one! That’s what lets GPS work so well – our cell phones and computers are using the same reference points as satellites orbiting the earth and can “talk” to each other in the same language to help us find our destination.