Latitude, Longitude, and Geographic Coordinates

Geographic coordinates are a pair of angles, latitude and longitude, that give the exact position of any point on Earth: latitude is the angle north or south of the equator (0° to 90°), and longitude is the angle east or west of the Prime Meridian (0° to 180°). In brief: lines of latitude (parallels) run east–west and are parallel to the equator; lines of longitude (meridians) run north–south from pole to pole. The equator divides Earth into the Northern and Southern Hemispheres, and the Prime Meridian and the 180° meridian divide it into the Eastern and Western Hemispheres. A location is written as latitude first, then longitude, for example 40° N, 75° W.

This system lets anyone describe a place without ambiguity and is the basis of maps, navigation and GPS. This guide explains map grids, latitude, longitude and the main reference lines, shows how to write and find coordinates, compares latitude and longitude in a table, works through examples with distances and time, outlines how the system developed and corrects common mistakes.

What is a map grid?

A grid (or graticule) is a network of crossing lines on a map that is used to give locations. On a globe or world map, the grid is made of lines of latitude and longitude. The point where a parallel and a meridian cross is the location of a place. The coordinates of the point are the angles of the two lines. Since Earth is nearly a sphere, positions are given as angles measured from the center of Earth, in degrees (°), minutes (′) and seconds (″), where 1° = 60′ and 1′ = 60″, or in decimal degrees (for example, 40.75° N).

What is latitude?

Latitude is the angular distance of a place north or south of the equator (0°), measured from Earth’s center. It runs from 0° at the equator to 90° N at the North Pole and 90° S at the South Pole. Lines of latitude are called parallels because they are parallel to each other, and each is a circle. The equator is the longest (about 40,075 km around), and the circles shrink toward the poles. One degree of latitude is about 111 km everywhere. Important parallels are the Tropic of Cancer (about 23.4° N), the Tropic of Capricorn (about 23.4° S), the Arctic Circle (about 66.6° N) and the Antarctic Circle (about 66.6° S). The equator divides Earth into the Northern Hemisphere and the Southern Hemisphere. Latitude is related to climate because it determines how directly the Sun’s rays reach the surface.

What is longitude?

Longitude is the angular distance of a place east or west of the Prime Meridian (0°), which passes through the Royal Observatory in Greenwich, London. It runs from 0° to 180° E and 0° to 180° W; the 180° meridian is roughly the basis of the International Date Line. Lines of longitude are called meridians, are half-circles of equal length from pole to pole, and meet at the poles. The distance of one degree of longitude is about 111 km at the equator, and decreases with the cosine of the latitude (about 79 km at 45°, about 56 km at 60°, and zero at the poles). The Prime Meridian and the 180° meridian divide Earth into the Eastern Hemisphere and the Western Hemisphere. Because Earth turns 360° in 24 hours, it turns 15° each hour, which is why the standard time zones are about 15° of longitude wide.

How do you write and find coordinates?

Write the latitude first, then the longitude, with the direction letter: 48° 51′ N, 2° 21′ E, or in decimal form with signs (north and east positive, south and west negative): 48.85, 2.35. To find a place on a map, find the parallel that matches the latitude, then the meridian that matches the longitude, and follow them until they cross. To find the coordinates of a place, read the nearest lines and estimate between them. Keep the hemispheres in mind: 30° N, 20° E is a different place from 30° S, 20° E.

Latitude and longitude compared

Worked example: distance, antipodes and time

1. North–south distance. Two places on the same meridian are at 30° N and 40° N. The difference is 10°, and 10 × 111 km = about 1,110 km (using Earth’s mean radius of 6,371 km, 1° = 111.2 km, so 1,112 km).
2. East–west distance. Two places at 60° N are 10° of longitude apart. One degree of longitude at 60° is 111.2 × cos 60° = 55.6 km, so the distance along the parallel is about 556 km, half of the distance for the same longitude difference at the equator (1,112 km).
3. Antipode. The point opposite to 30° N, 20° E on the globe has the opposite latitude (30° S) and the longitude changed by 180°: 20° E − 180° = −160°, which is 160° W. The antipode is 30° S, 160° W.
4. Time zone. A place at 75° W is 75 ÷ 15 = 5 hours behind the Prime Meridian in solar time, so when it is noon at Greenwich, the mean solar time there is 7:00 a.m. (legal time zones are adjusted by governments).
5. Writing coordinates. 40.75° N, 74.00° W in degrees and minutes is 40° 45′ N, 74° 00′ W, because 0.75 × 60 = 45′.

How did the system develop?

The Greeks, notably Eratosthenes and Hipparchus, divided the globe into a grid, and Ptolemy listed coordinates for many places. Latitude is easy to find from the height of the Sun at noon or the Pole Star. Longitude required accurate timing: an observer needs the local time and the time at a reference meridian. The problem was solved in the 18th century by John Harrison’s marine chronometer. Many countries used their own prime meridians until an international conference in Washington in 1884 chose the Greenwich meridian. Satellite systems such as GPS now give coordinates to a few meters or better.

Which mistakes are common?

Mistake 1: Reversing the order of latitude and longitude

Latitude (north–south) comes first. Reversing them can put the place in a different part of the world.

Mistake 2: Leaving out N/S or E/W

Without the direction letters (or the signs), the hemisphere is unknown.

Mistake 3: Believing that lines of latitude meet at the poles

Parallels never meet. It is the meridians that converge at the poles.

Mistake 4: Treating a degree of longitude as a fixed distance

The distance varies with latitude, from about 111 km at the equator to zero at the poles.