To find a point on a coordinate plane, you give two numbers. A globe works the same way, with angles instead of distances. The two numbers are latitude and longitude.
- Latitude tells how far north or south of the equator a place is, from 0° at the equator to 90° at each pole. Lines of latitude run east and west in rings that never meet.
- Longitude tells how far east or west of the prime meridian (through Greenwich, England) a place is, from 0° to 180°. Lines of longitude run from pole to pole, and they all meet at the poles.
Key idea
Write latitude first, then longitude, each with its direction: New Orleans is at about 30° N, 90° W. Latitude says north or south; longitude says east or west.
Why it works
The equator and the prime meridian act like the x- and y-axes. North and east are like positive numbers, south and west like negative ones, so 30° S, 60° W can also be written (−30, −60). The angles are measured from Earth's center, which is why they stop at 90° (a pole) and 180° (halfway around).
Worked example: Reading a place
Buenos Aires is about 34° south of the equator and 58° west of the prime meridian. Write its location.
- Latitude comes first: 34° S.
- Longitude second: 58° W.
Answer: 34° S, 58° W
Worked example: How far apart?
Two towns lie on the same line of longitude, one at 20° N and one at 15° S. How many degrees of latitude apart are they?
- They are on opposite sides of the equator.
- From 20° N down to the equator is 20°, then 15° more to 15° S.
- $20 + 15 = 35$ degrees. (Each degree of latitude is about 111 km, so that is about 3,900 km.)
Answer: 35°
Common mistake
Swapping the two, or mixing up which lines meet. Latitude lines are like the rungs of a ladder ("lat" sounds like ladder), parallel and never meeting. Longitude lines are long, running pole to pole, and they all meet at the poles. Check: a latitude can never be more than 90°.