Latitude and Longitude

Latitude and longitude form a geographic coordinate system. Latitude specifies the north-south position of a point on Earth, while longitude defines its east-west position. Latitude lines run east–west around the Earth and remain parallel to each other. Longitude lines run north–south from pole to pole. These lines are not parallel, so they are furthest apart at the equator and closest near the poles. Lines of latitude and longitude form a model called a graticule.

Latitude

Latitude (ϕ or phi) specifies the north-south position of a point on the Earth’s surface. Lines of latitude encircle the Earth, running parallel to the equator, so they are also called parallels. Latitude values range from 0° at the equator to 90° north at the North Pole and 90° south at the South Pole.

Lines of Latitude

Technically, there are many lines of latitude or parallels that divide the Earth. While there are 180° of latitude, not all of the lines neatly fall onto degrees. There are 7 main lines of latitude:

• Equator (0°)
• Tropic of Cancer (23.5° N) – 23.44° precisely
• Tropic of Capricorn (23.5° S) – 23.44° precisely
• Arctic circle (66.5° N)
• Antarctic circle (66.5° S)
• North Pole (90° N)
• South Pole (90° S)

There are 5 main lines of latitude if you omit the North Pole and South Pole, which are really points rather than lines.

The orientation of latitude lines reflects Earth’s rotational axis. The equator lies in a plane perpendicular to Earth’s axis. Because Earth’s axis is tilted about 23.5° relative to the plane of its orbit around the Sun (the ecliptic), the equatorial plane is tilted by the same amount relative to the ecliptic. At the equinoxes the Sun lies directly above the equator, while at the solstices the Sun reaches its maximum declination of about ±23.5°, defining the Tropic of Cancer and Tropic of Capricorn.

Longitude

Longitude (λ or lambda) specifies the east-west position of a point on the Earth’s surface. Each line of longitude runs from pole to pole and is called a meridian. The Prime Meridian (0° longitude) passes through the Royal Observatory in Greenwich, England, which serves as the international reference for longitude. Longitude runs 180° east and 180° west. In addition to location, longitude also defines Greenwich Mean Time.

Latitude vs Longitude (Quick Comparison)

How Big Are Latitude and Longitude Degrees?

Because lines of latitude are parallel to each other, each degree represents the same distance. Each degree of latitude is about 111 kilometers (69 miles or 364,000 feet). A second of latitude is about 30.7 meters (101 feet). Because Earth is slightly flattened at the poles (an oblate spheroid), the distance represented by one degree of latitude varies slightly, from about 110.6 km at the equator to 111.7 km near the poles.

Degrees of longitude vary. They are largest at the equator and smallest near the poles. The degrees of longitude are 111 kilometers (69 miles) apart at the equator. At 38 degrees of latitude (North or South), one degree of longitude is about 88 kilometers (54.6 miles or 288,200 feet), one minute is 1463 meters (just under 1 mile or 4800 feet), and one second is 24 meters (80 feet). Right at the poles, the degrees are 0 meters or feet.

How to Read Latitude and Longitude (GPS Coordinates)

Map coordinates given in latitude and longitude use a geographic coordinate system or GPS. Be aware there are actually multiple methods that use latitude and longitude and give slightly different positions. The most common methods are the Degrees, Minutes, Seconds (DMS) and Decimal Degree (DD) systems.

GPS coordinates give latitude first, followed by longitude. A comma or space separates the two values. For example, coordinates of 10°N, 70°W specify a location that is 10° north of the equator and 70° west of Greenwich, England. These are the map coordinates for a location in Venezuela.

Most locations do not lie directly on either a line of latitude or longitude. A DMS location uses degrees (°), minutes (‘), and seconds (“). The degrees and minutes values are whole numbers, while seconds are a decimal value. For example, writing the coordinates 10°00’00.0”N, 70°00’00.0”W means exactly the same thing as 10°N, 70°W.

In decimal degrees (DD), the coordinate is written as a decimal number rather than degrees, minutes, and seconds. Positive latitude values indicate locations north of the equator, while negative values indicate south of the equator. Positive longitude values indicate locations east of the Prime Meridian, while negative values indicate west.

For example:

41.40338, 2.17403

This coordinate refers to a location in Barcelona, Spain.

Geographic Coordinate System

Latitude and longitude together form the geographic coordinate system, which allows any point on Earth’s surface to be identified with numerical coordinates. The system divides the planet using a grid called a graticule, consisting of parallels (latitude lines) and meridians (longitude lines).

Unlike flat coordinate systems such as the Cartesian grid, geographic coordinates describe positions on a spherical surface. Because of this curvature, distances and directions must account for Earth’s shape when used in navigation or mapping.

This coordinate system is fundamental to navigation, cartography, geographic information systems (GIS), satellite positioning, and global mapping technologies.

History

Eratosthenes of Cyrene gets credit for inventing the geographic coordinate system, which he described in his Geography text in the 3rd century BC. Marinus of Tyre plotted a map of the known world using latitude and longitude in the 1st or 2nd century. Ptolemy’s Geography (2nd century) used the Equator for measuring latitude and a prime meridian off the coast of western Africa. The Prime Meridian was placed at the Royal Observatory in Greenwich, England following an international vote in 1884.

Why Longitude Was Difficult to Measure

Determining latitude historically was relatively straightforward because it can be measured using the altitude of the Sun or stars above the horizon. Longitude was much harder to determine.

Accurate longitude requires knowing the difference between local time and the time at a reference location, such as the Prime Meridian. Before the invention of precise portable clocks, sailors had difficulty determining longitude at sea.

The problem was solved in the 18th century with the development of the marine chronometer by John Harrison, which allowed navigators to carry accurate time from Greenwich. This breakthrough made precise global navigation possible.

Latitude, Longitude, and Time Zones

Longitude also forms the basis of the global time system. Because Earth rotates 360° in about 24 hours, the planet turns approximately 15° of longitude per hour.

Modern time zones divide the Earth into regions roughly 15° wide, each representing one hour of time difference. The Prime Meridian at Greenwich serves as the reference for Greenwich Mean Time (GMT) and Coordinated Universal Time (UTC).

Although time zones follow longitude in principle, political boundaries often cause them to deviate significantly from the ideal 15° divisions.

References

• Chang, Kang-tsung (2016). Introduction to Geographic Information Systems (9th ed.). McGraw-Hill. ISBN 978-1-259-92964-9.
• Evans, James (1998). The History and Practice of Ancient Astronomy. Oxford, England: Oxford University Press. ISBN 9780199874453.
• McPhail, Cameron (2011). Reconstructing Eratosthenes’ Map of the World. Dunedin, New Zealand: University of Otago.
• Mittenhuber, Florian (2010). “The Tradition of Texts and Maps in Ptolemy’s Geography”. In Jones, Alexander (ed.). Ptolemy in Perspective: Use and Criticism of his Work from Antiquity to the Nineteenth Century. Archimedes. Vol. 23. Dordrecht: Springer. ISBN 978-90-481-2787-0. doi:10.1007/978-90-481-2788-7_4
• Torge, W. (2001). Geodesy (3rd ed.). De Gruyter. ISBN 3-11-017072-8.