In Halves of the World you met two famous lines: the equator, around the middle of Earth, and the prime meridian, from the North Pole to the South Pole. Mapmakers draw many more lines like them. Together they make a net, or grid, that covers the whole globe.
Key idea
Parallels (lines of latitude) are circles that run east and west around the globe. Meridians (lines of longitude) are half circles that run north and south, from pole to pole.
Why it works
Parallels are called that because they never meet: like the rails of a train track, they stay the same distance apart all the way around. Meridians all meet at the North Pole and the South Pole, like the lines between the sections of an orange. So they are far apart at the equator and squeeze together near the poles.
| Parallels (latitude) | Meridians (longitude) | |
|---|---|---|
| Which way they run | East and west | North and south |
| What they measure | How far north or south | How far east or west |
| Where they start | The equator, 0° | The prime meridian, 0° |
| Do they meet? | Never | At both poles |
| Length | Shorter toward the poles | All the same length |
Worked example: Which line is which?
A line runs from the North Pole straight down to the South Pole. Is it a parallel or a meridian? What does it help you measure?
- It runs north and south, from pole to pole.
- Lines from pole to pole are meridians.
- Meridians are used to measure how far east or west a place is.
Answer: A meridian. It measures east-west position (longitude).
Worked example: The tricky part
Parallels run east and west. So do they measure how far east you are?
- Walk along one parallel: you go east or west, but your distance from the equator stays the same.
- Step from one parallel to the next: now you have moved north or south.
- So the parallel you are on tells how far north or south you are.
Answer: No. Parallels measure north-south position (latitude), even though they run east-west.
Common mistake
Many people mix the two up because of the directions. Parallels run east-west but measure north-south; meridians run north-south but measure east-west. A check that works: latitude lines lie flat, like the rungs of a ladder (a "ladder-tude"), and you climb a ladder up and down, north and south.