Definition:Latitude (Terrestrial)

Definition
Let $J$ be a point on Earth's surface that is not one of the two poles $N$ and $S$.

Let $\bigcirc NJS$ be a meridian passing through $J$, whose endpoints are by definition $N$ and $S$.

Let $\bigcirc NJS$ pass through the equator at $L$.

The latitude of $J$ is the (spherical) angle $\sphericalangle LOJ$, where $O$ is the center of Earth.

If $J$ is in the northern hemisphere of Earth, the latitude is defined as latitude $n \degrees$ north, where $n \degrees$ denotes $n$ degrees (of arc), written $n \degrees \, \mathrm N$.

If $J$ is in the southern hemisphere of Earth, the latitude is defined as latitude $n \degrees$ south, written $n \degrees \, \mathrm S$.

At the North Pole, the latitude is $90 \degrees \, \mathrm N$.

At the South Pole, the latitude is $90 \degrees \, \mathrm S$.

Also see

 * Definition:Latitude (Celestial)