By David Chandler | Updated March 24 2022
Lines of latitude are imaginary great circles that indicate how far a point on Earth lies north or south of the Equator. Latitude is expressed in degrees, minutes, and seconds, with the Equator at 0° and the North and South Poles at 90° N and 90° S respectively. Combined with longitude, latitude provides a precise geographic coordinate for any location.
Although the planet is not a perfect sphere—its equatorial radius is slightly larger than the polar radius—it can be approximated as a sphere for most practical purposes. A sphere’s surface is divided into 360° of latitude, allowing us to map every point with a unique pair of angles.
Latitude lines run east‑west and measure north‑south position, while longitude lines run north‑south and measure east‑west displacement from a chosen reference. Together, they form a grid that enables accurate navigation and mapping.
The Equator serves as the zero‑degree reference for latitude, equidistant from both poles. For longitude, the Prime Meridian (Greenwich Line) marks 0°, with values increasing eastward or westward. These standards underpin global coordinate systems used by GPS, aviation, and maritime navigation.
Because Earth’s axis is tilted, several latitudes have earned specific names:
Latitude’s relation to the Equator simplifies celestial navigation. The North Star (Polaris) lies almost directly above the North Pole; its altitude above the horizon equals a ship’s latitude in the Northern Hemisphere. At the Equator, Polaris appears near the horizon (0° altitude). Similar principles apply to other stars, enabling sailors to determine latitude before modern electronic aids.
