Geographic coordinate systems use an imaginary grid, known as a graticule, to identify every location on the planet’s surface. This grid serves as the foundation for modern navigation and mapping. The system relies on a pair of angular measurements—latitude and longitude—that function like an address, providing a universal method for defining a point. Although different in construction, these two measurements must be used together to define a singular spot.
Understanding Latitude
Latitude measures a location’s distance north or south of the Equator. The lines used to denote latitude are called parallels because they run horizontally around the globe, parallel to the Equator. These lines are concentric circles that decrease in circumference as they approach the poles.
The Equator is the reference line for all latitude, designated as 0 degrees, which divides the Earth into the Northern and Southern Hemispheres. Latitude is measured in degrees, ranging from 0° at the Equator to 90° North or 90° South at the poles. Since the parallels are always equidistant, the physical distance between any two degrees of latitude remains relatively constant across the globe.
Understanding Longitude
Longitude measures a location’s distance east or west of a reference line. The lines of longitude are called meridians, and they run vertically from the North Pole to the South Pole. Unlike parallels, all meridians are halves of great circles and are the same length.
The reference line is the Prime Meridian, designated as 0 degrees longitude, which passes through the Royal Observatory in Greenwich, England. Longitude is measured from 0° eastward or westward up to 180°. The 180° meridian, opposite the Prime Meridian, is known as the International Date Line.
Meridians converge and meet at both the North and South Poles. Consequently, the physical distance represented by one degree of longitude is widest at the Equator (approximately 111.3 kilometers) and narrows to zero at the poles. This converging characteristic links longitude to time measurement, as the Earth rotates 360 degrees over 24 hours.
Key Differences Between Latitude and Longitude
A fundamental distinction lies in the reference points. Latitude uses the Equator as its 0° baseline, which is a naturally occurring midpoint defined by the Earth’s rotation. Longitude uses the Prime Meridian, a line arbitrarily selected by international agreement to pass through Greenwich, England.
The physical geometry of the lines also differs significantly. Lines of latitude are parallel circles of varying size that never meet, ensuring the distance between parallels remains consistent. Conversely, lines of longitude are semicircles of equal size that meet at the poles, meaning the distance between meridians changes based on the distance from the Equator.
The measurements describe different directions on the Earth’s surface. Latitude specifies angular distance North or South relative to the poles, influencing climate and solar exposure. Longitude specifies angular distance East or West relative to the Prime Meridian, directly relating to the establishment of global time zones.
How Coordinates Pinpoint Location
Both latitude and longitude are required to form a precise geographic address, as neither coordinate can define a unique location alone. The combination of a latitude line and a longitude line creates a grid system where the lines intersect at right angles, forming a singular point known as the coordinate.
Coordinates are conventionally expressed with the latitude value stated first, followed by the longitude value. For example, 40° N, 74° W indicates a position 40 degrees north of the Equator and 74 degrees west of the Prime Meridian. The origin point of the system (0° latitude and 0° longitude) is located in the Atlantic Ocean in the Gulf of Guinea.
For greater accuracy, degrees are further subdivided using the sexagesimal system. Each degree is divided into 60 minutes of arc (‘), and each minute is further divided into 60 seconds of arc (“). This allows for a precision that can define a location within meters.