Circle of latitude
Imaginary east–west lines parallel to the Equator.
A circle of latitude, or line of latitude, is an abstract east–west small circle on Earth connecting all locations at a given latitude coordinate, ignoring elevation. Often called parallels because they are parallel to each other, these circles are fundamental to geographic coordinate systems and mapmaking. Their length decreases with distance from the Equator, which is the longest circle of latitude and the only one that is also a great circle.
- type
- Geographic concept
- key_feature
- Parallel east–west circles at constant latitude
- longest_circle
- Equator (0° latitude)
- major_circles
- Arctic Circle, Tropic of Cancer, Equator, Tropic of Capricorn, Antarctic Circle
- number_of_integral_circles
- 89 between Equator and each pole per hemisphere
- used_for
- Defining borders and geographical zones
Lore & Background
Circles of latitude are defined as small circles on Earth's surface, with the Equator being the sole great circle among them. Their lengths follow a cosine function; for instance, the 60th parallel is half as long as the Equator. On maps, their appearance varies by projection: on an equirectangular projection they are horizontal, parallel, and equally spaced, while on a Mercator projection they are more widely spaced near the poles to preserve local shapes, and on a Gall–Peters projection they are spaced more closely near the poles for accurate area comparisons. On most non-cylindrical projections, they are neither straight nor parallel.
Reader's Guide
Circles of latitude serve as essential reference lines for navigation, mapping, and defining political boundaries. They are often used as borders where natural features are absent, such as the northern border of Colorado at 41° N and the southern border at 37° N, or roughly half the U.S.–Canada border along 49° N. The five major circles—Arctic Circle, Tropic of Cancer, Equator, Tropic of Capricorn, and Antarctic Circle—mark divisions between principal geographical zones. Shorter-term variations from nutation and polar motion also cause small daily shifts. On other planets, analogous circles can be defined based on axial tilt.
Did You Know?
- The Equator is the only circle of latitude that is also a great circle.
- The 60th parallel north or south is half as long as the Equator, because cos(60°) = 0.5.
- The positions of the Tropical and Polar Circles are not fixed; they shift due to changes in Earth's axial tilt.
- Arcs of circles of latitude are sometimes used as boundaries between countries or regions where natural borders are lacking.
Frequently Asked Questions
What is a circle of latitude?
A circle of latitude is an imaginary east–west line that wraps around Earth at a fixed angular distance from the Equator. Every point on that line shares the same north–south coordinate, and all such lines run parallel to one another.
Why is the Equator unique among all circles of latitude?
The Equator at 0° is the longest parallel because it is the only one that also counts as a great circle. Every other parallel shrinks in circumference the farther it stretches toward the poles.
What are the five most well-known circles of latitude?
The five major named parallels are the Arctic Circle, Tropic of Cancer, Equator, Tropic of Capricorn, and Antarctic Circle. Together they mark key boundaries for seasonal daylight extremes and broad climate zones.
What practical purposes do circles of latitude serve?
Parallels underpin geographic coordinate systems, making them essential for navigation, map projection, and drawing political borders. They also define climatic and seasonal zones such as the tropics and polar regions.
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