Pinpointing any location on Earth relies on a system of coordinates using an intersecting network of imaginary lines drawn onto maps and globes. A fundamental component of this geographic grid is the parallel, an imaginary line that establishes a precise north-south position. Parallels are used in conjunction with other reference lines to assign an exact address to every point on the planet’s surface.
Defining Lines of Latitude
A parallel is a line of latitude, an imaginary line encircling the Earth in an east-west direction. These lines are termed “parallels” because they remain equidistant from one another and never intersect. They are always parallel to the Equator, the longest of these circles, which wraps around the middle of the planet. Every point along a single parallel shares the exact same distance north or south of the Equator.
Geometrically, parallels are circles that become progressively smaller as they move away from the Equator toward the North and South Poles. The Equator is a “great circle” because it divides the Earth into two equal hemispheres, but all other parallels are “small circles.” The consistent spacing means the distance between any two adjacent parallels remains nearly constant at approximately 69 miles (111 kilometers) per degree.
The System of Measurement
Parallels represent latitude, which is measured in degrees to indicate a location’s distance from the Equator. The Equator is the reference point, designated as 0 degrees latitude. Lines of latitude are numbered from 1 degree up to 90 degrees North (N) and 90 degrees South (S). The poles represent the maximum latitude at 90 degrees North and 90 degrees South.
For highly precise location, each degree of latitude is subdivided into 60 minutes, and each minute into 60 seconds. Certain parallels hold specific designations because they relate to the Earth’s orbit and axial tilt, which influence climate.
Major Designated Parallels
These lines mark important climatic boundaries:
- The Tropic of Cancer (approximately 23.5° N).
- The Tropic of Capricorn (approximately 23.5° S).
- The Arctic Circle (roughly 66.5° N).
- The Antarctic Circle (roughly 66.5° S).
How Parallels Differ from Meridians
A complete coordinate requires both latitude and longitude, which relies on a separate set of lines known as meridians. Meridians are imaginary lines that run north and south, connecting the North Pole to the South Pole. This direction contrasts sharply with parallels, which run horizontally from east to west. While parallels are parallel to each other, meridians are not; they are farthest apart at the Equator and converge at both poles.
Meridians measure longitude, indicating a location’s distance east or west of the Prime Meridian. This reference line is designated as 0 degrees, passes through Greenwich, England, and divides the globe into the Eastern and Western Hemispheres. When parallels and meridians are overlaid on a map, they intersect at right angles, forming the grid system that allows for the unique identification of every point on Earth.