What Are GPS Coordinates? Latitude and Longitude Explained

GPS coordinates are a pair of numbers — latitude and longitude — that describe an exact position on the surface of the Earth. Together they work like a global address system: no two points share the same pair, and any device that understands them can locate that exact spot, anywhere on the planet, with no local knowledge required.

Latitude: how far north or south

Latitude measures the angle between a point, the centre of the Earth, and the equator. The equator itself is 0°, the North Pole is 90°N, and the South Pole is 90°S. Because latitude lines (parallels) run east-west and are evenly spaced, one degree of latitude is always close to 111 km, no matter where on Earth you are.

Longitude: how far east or west

Longitude measures the angle east or west of the Prime Meridian, the 0° line that passes through Greenwich, London, by international agreement. Longitude runs from 0° to 180°E and 0° to 180°W. Unlike latitude, the real-world distance covered by one degree of longitude shrinks as you move away from the equator, since the meridians converge at the poles — at the equator it is about 111 km, but near the poles it approaches zero.

How precise does a coordinate need to be?

Coordinates are usually written as decimal degrees, such as 51.477850, -0.001470. Each decimal place roughly corresponds to a real-world distance at the equator:

• 1 decimal place ≈ 11.1 km — distinguishes one town from another
• 3 decimal places ≈ 111 m — distinguishes one city block from another
• 5 decimal places ≈ 1.1 m — precise enough to identify an individual building or tree
• 6+ decimal places — beyond the accuracy of most consumer GPS hardware

A coordinate is only as useful as the format the person reading it expects.

The three formats you'll actually see

The same point can be written as Decimal Degrees (DD), Degrees Minutes Seconds (DMS), or Degrees Decimal Minutes (DDM). DD is what apps, databases and APIs expect; DMS is what you'll see on paper maps and surveying documents; DDM is the convention in marine and aviation navigation. If you regularly convert between them by hand, it's worth reading our companion guide on the differences between the three.