51.5°N 0.0°Greenwich, London
Latitude: north and south
Latitude measures how far a place is north or south of the equator, as an angle from Earth's center. The equator is 0°, the North Pole is 90°N and the South Pole is 90°S. Lines of latitude are called parallels because they never meet: they are circles that get smaller toward the poles.
A degree of latitude is about 111 km (69 miles) everywhere, give or take a little because Earth is slightly flattened at the poles.
Longitude: east and west
Longitude measures how far a place is east or west of the prime meridian, the line of 0° that runs through the Royal Observatory in Greenwich, London. It was chosen as the world's reference at the International Meridian Conference in 1884. Longitude runs up to 180° east and 180° west, which meet on the opposite side of the world in the Pacific.
Lines of longitude are called meridians. They run from pole to pole and come together at both poles, so the distance covered by one degree of longitude shrinks as you move away from the equator.
| Latitude | Kilometers (about) | Miles (about) | Share of the equator width |
|---|---|---|---|
| 0° | 111 | 69 | |
| 30° | 96 | 60 | |
| 45° | 79 | 49 | |
| 60° | 56 | 35 | |
| 80° | 19 | 12 | |
| 90° | 0 | 0 |
This is why a square grid cell on a globe is really a narrowing wedge, and why world maps have to make a choice about how to draw it. See map projections for what that choice does.
Degrees, minutes and seconds
Each degree splits into 60 minutes (′), and each minute into 60 seconds (″). One minute of latitude is about 1.85 km, which is where the nautical mile comes from. One second is about 31 m (100 ft).
Phones and online maps usually show decimal degrees instead. In decimal form, south latitudes and west longitudes are written as negative numbers, so 33.9° S, 151.2° E becomes -33.9, 151.2.
How to convert to decimal degrees
- Take the minutes and divide by 60. For 40° 26′ 46″ N, 26 ÷ 60 = 0.4333.
- Take the seconds and divide by 3,600. 46 ÷ 3,600 = 0.0128.
- Add them to the degrees: 40 + 0.4333 + 0.0128 = 40.4461.
- Make the number negative if it is south or west. This one is north, so it stays 40.4461.
Latitude comes first by convention. If a pair of coordinates puts you in the ocean, the two numbers may have been swapped or a minus sign dropped.
How precise is a coordinate?
| Decimal places | Example | Precision on the ground (about) |
|---|---|---|
| 1 | 51.5 | 11 km: a city |
| 2 | 51.48 | 1.1 km: a neighborhood |
| 3 | 51.477 | 110 m: a large building |
| 4 | 51.4769 | 11 m: a house |
| 5 | 51.47691 | 1.1 m: a person |
The figures are for latitude. For longitude, the same number of decimals gets more precise as you go toward the poles, for the reason in the table above. The coordinate tags on this site use one decimal place, which is enough to find the right area on a map.
Special parallels
The tropics sit at about 23.4° north and south, matching the tilt of Earth's axis. Between them the sun is directly overhead at least once a year. The Arctic and Antarctic Circles sit at about 66.6°, and beyond them there is at least one day a year of midnight sun. The climate zones post shows how these lines line up with broad climate belts.
Latitude and longitude FAQ
Which comes first, latitude or longitude?
Latitude, then longitude, in most maps, apps and textbooks. Some software formats reverse the order, so check the documentation when you paste coordinates between tools.
Why is the prime meridian in Greenwich?
It was agreed at an international conference in 1884, partly because many sea charts already used Greenwich as their zero line. Any meridian could have worked, since longitude has no natural starting point the way the equator does for latitude.
Is there a place at 0° latitude and 0° longitude?
Yes, in the Gulf of Guinea off West Africa, in open ocean. Mapping software often puts data there by mistake when coordinates are missing, which is a handy sign of an error.