Latitude And Longitude | Definition, Examples, Diagrams, & Facts

Technical considerations

Technically speaking, there are different kinds of latitude—geocentric, astronomical, and geographic (or geodetic)—but there are only minor differences between them. In most common references, geocentric latitude is implied. Given in degrees, minutes, and seconds, geocentric latitude is the arc (a curved line) that can be drawn along Earth’s surface, created by an imaginary plane that passes through Earth’s center, whose angle diverges from that of the equatorial plane (that is, the imaginary plane that cuts through Earth and includes all points along the Equator). Thus, a point at 30°15′20″ N is the arc that results from an angle of 30°15′20″ at the center of the globe. Astronomical latitude is the angle created by the equatorial plane and a line created by the direction of gravity (that is, the plumb line) occurring at a given point on Earth’s surface.

Geographic latitude, which is the kind used in mapping, is calculated using a slightly different process. In perfect spheres, geocentric latitude would be the arc and the normal line that can be drawn from a given point on Earth’s surface to Earth’s center. Because Earth is not a perfect sphere—the planet’s curvature is flatter at the poles—geographic latitude is the arc resulting from an angle created by the equatorial plane and the normal line; the normal line does not travel through Earth’s center. (The normal line is perpendicular to a tangent line touching Earth’s curvature at that point on the surface.) Different methods are used to determine geographic latitude, as by taking angle-sights on certain polar stars or by measuring with a sextant the angle of the noon Sun above the horizon. The length of a degree of arc of latitude is approximately 111 km (69 miles), varying, because of the nonuniformity of Earth’s curvature, from 110.567 km (68.703 miles) at the Equator to 111.699 km (69.41 miles) at the poles. Geographic latitude is also given in degrees, minutes, and seconds.

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In contrast, longitude is the amount of arc created by drawing first a line from Earth’s center to the intersection of the Equator and the prime meridian and then another line drawn from Earth’s center to any point elsewhere along the Equator. Since lines of longitude are not parallel to one another, the distance between one degree of longitude and the next will vary significantly depending upon how close to the poles the measurement is taken. The distance per degree of longitude at the Equator is about 111.32 km (69.17 miles) and at the poles, 0.