Editing Latitude (section)

==Background==
Two levels of abstraction are employed in the definitions of latitude and longitude. In the first step the physical surface is modeled by the [[geoid]], a surface which approximates the [[Sea level|mean sea level]] over the oceans and its continuation under the land masses. The second step is to approximate the geoid by a mathematically simpler reference surface. The simplest choice for the reference surface is a [[sphere]], but the geoid is more accurately modeled by an [[ellipsoid of revolution]]. The definitions of latitude and longitude on such reference surfaces are detailed in the following sections. Lines of constant latitude and longitude together constitute a [[Geographic coordinate system|graticule]] on the reference surface. The latitude of a point on the ''actual'' surface is that of the corresponding point on the reference surface, the correspondence being along the [[Normal (geometry)|normal]] to the reference surface, which passes through the point on the physical surface. Latitude and longitude together with some specification of [[Altitude|height]] constitute a [[geographic coordinate system]] as defined in the specification of the ISO 19111 standard.<ref>{{cite web|title=ISO 19111 Geographic information — Referencing by coordinates|url=https://committee.iso.org/sites/tc211/home/projects/projects---complete-list/iso-19111.html|access-date=2022-01-16|website=ISO|date=2021-06-01}}</ref>

Since there are many different [[reference ellipsoid]]s, the precise latitude of a feature on the surface is not unique: this is stressed in the ISO standard which states that "without the full specification of the coordinate reference system, coordinates (that is latitude and longitude) are ambiguous at best and meaningless at worst". This is of great importance in accurate applications, such as a [[Global Positioning System]] (GPS), but in common usage, where high accuracy is not required, the reference ellipsoid is not usually stated.

In English texts, the latitude angle, defined below, is usually denoted by the Greek lower-case letter [[phi (letter)|phi]] ({{mvar|ϕ}} or {{mvar|φ}}). It is measured in [[Degree (angle)|degrees]], [[arcminute|minutes and seconds]], or [[decimal degrees]], north or south of the equator. For navigational purposes positions are given in degrees and decimal minutes. For instance, [[The Needles]] lighthouse is at 50°39.734′ N 001°35.500′ W.<ref>{{cite web|author= The Corporation of Trinity House |title=1/2020 Needles Lighthouse|date=10 January 2020|series=Notices to Mariners|url=https://www.trinityhouse.co.uk/notice-to-mariners/1/2020-needles-lighthouse|access-date=24 May 2020}}</ref>
<!--The latitude of a point on the reference surface is defined as the angle between the [[Surface normal|normal]] to the reference surface (at the point in question) and the equatorial plane. A corollary of this definition is that the latitude angle of a point on the reference surface is not unique: it depends on the precise choice of the reference surface. -->

This article relates to coordinate systems for the Earth: it may be adapted to cover the Moon, planets and other celestial objects ([[planetographic latitude]]).

For a brief history, see [[History of latitude]].

===Determination===
{{see also|Longitude determination}}
{{further|Celestial navigation#Latitude}}

In [[celestial navigation]], latitude is determined with the [[meridian altitude]] method.
More precise measurement of latitude requires an understanding of the gravitational field of the Earth, either to set up [[theodolite]]s or to determine GPS satellite orbits. The study of the [[figure of the Earth]] together with its gravitational field is the science of [[geodesy]].
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