Circle of latitude
Abstract east–west parallels defining Earth's latitudinal grid.
A circle of latitude, also known as a parallel, is an imaginary line that runs east–west around the Earth, connecting all points that share the same latitude coordinate while disregarding elevation. These circles are termed parallels because they are all parallel to one another; the planes containing any two such circles never intersect. A location’s position along a given circle of latitude is specified by its longitude. Unlike circles of longitude, which are great circles with the Earth’s center at their midpoint, circles of latitude shrink in size as one moves away from the Equator. Their length can be determined using a sine or cosine function; for instance, the 60th parallel north or south is half the length of the Equator, ignoring the Earth’s minor flattening of about 0.335%. On projections such as the Mercator or Gall-Peters, a circle of latitude is perpendicular to all meridians. On an ellipsoid or spherical projection, every circle of latitude except the Equator is a rhumb line.
The latitude of a circle is approximately the angle measured at Earth’s center between the Equator and that circle. The Equator lies at 0°, while the North and South Poles are at 90° north and 90° south, respectively. The Equator is the longest circle of latitude and the only one that is also a great circle, making it perpendicular to all meridians. Between the Equator and each pole, there are 89 integral (whole-degree) circles of latitude, though latitude can be subdivided into decimal degrees or minutes and seconds (e.g., 34.637° N or 22°14′26″ S).
On maps, the appearance of circles of latitude depends on the projection used. In an equirectangular projection centered on the equator, they appear as horizontal, parallel, and equally spaced lines. On other cylindrical and pseudocylindrical projections, they remain horizontal and parallel but may be unevenly spaced to achieve specific map properties—for example, on a Mercator projection they are spaced farther apart near the poles to preserve local shapes, while on a Gall-Peters projection they are spaced more closely near the poles to ensure accurate area comparisons. On most non-cylindrical and non-pseudocylindrical projections, circles of latitude are neither straight nor parallel.
Arcs of circles of latitude are frequently used as political boundaries where natural borders are absent, such as in deserts, or where an ar
- type
- Geographic concept
- key_circles
- Equator, Tropic of Cancer, Tropic of Capricorn, Arctic Circle, Antarctic Circle
- number_of_integral_circles
- 89 per hemisphere between Equator and poles
- basis
- Angle between Equator and circle, vertex at Earth's centre
Lore & Background
Circles of latitude are often called parallels because planes containing any of these circles never intersect each other. A location's position along a circle of latitude is given by its longitude. Unlike circles of longitude, which are all great circles with Earth's centre in the middle, circles of latitude get smaller as distance from the Equator increases; for example, the 60th parallel north or south is half as long as the Equator, stemming from cos(60°) = 0.5. On the Mercator or Gall-Peters projection, a circle of latitude is perpendicular to all meridians, and on the ellipsoid or spherical projection, all circles of latitude are rhumb lines except the Equator.
Reader's Guide
Circles of latitude are essential for geographic orientation, mapping, and defining climatic zones. The five major circles—Arctic Circle, Tropic of Cancer, Equator, Tropic of Capricorn, and Antarctic Circle—mark divisions between principal geographical zones. Arcs of circles of latitude are sometimes used as boundaries between countries or regions where natural borders are lacking, such as the northern border of Colorado at 41° N and the southern border at 37° N, and roughly half the length of the border between the United States and Canada follows 49° N. On maps, their appearance varies by projection: on equirectangular projection they are horizontal, parallel, and equally spaced; on Mercator they are more widely spaced near poles; on Gall-Peters they are spaced more closely near poles; on most non-cylindrical projections they are neither straight nor parallel.
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, due to cos(60°) = 0.5.
- The positions of the Tropical and Polar Circles are not fixed; they drift by about 15 m per year due to changes in Earth's axial tilt.
- Arcs of circles of latitude are sometimes used as boundaries, such as the 49° N border between the United States and Canada.
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