The fundamental plane in a spherical coordinate system is a plane which divides the sphere into two hemispheres. The latitude of a point is then the angle between the fundamental plane and the line joining the point to the centre of the sphere. A point plotted using the spherical coordinate system In mathematics, the spherical coordinate system is a coordinate system for representing geometric figures in three dimensions using three coordinates: the radial distance of a point from a fixed origin, the zenith angle from the positive z-axis, and the azimuth angle... Look up plane in Wiktionary, the free dictionary. ... A sphere is a symmetrical geometrical object. ... The word hemisphere literally means half sphere or half ball; when used in the singular form, it refers to one of the halves of a spherical object. ... This article is about the geographical term. ... Point can refer to: Look up Point in Wiktionary, the free dictionary // Mathematics In mathematics: Point (geometry), an entity that has a location in space but no extent Fixed point (mathematics), a point that is mapped to itself by a mathematical function Point at infinity Point group Point charge, an... This article is about angles in geometry. ...

For a geographic coordinate system of the Earth, the fundamental plane is the equator. Celestial coordinate systems have varying fundamental planes: Map of Earth showing lines of latitude (horizontally) and longitude (vertically), Eckert VI projection; large version (pdf, 1. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ... In astronomy, a celestial coordinate system is a coordinate system for mapping positions in the sky. ...

• the equatorial coordinate system uses the celestial equator;
• the ecliptic coordinate system uses the ecliptic;
• the galactic coordinate system uses the Milky Way; and
• the horizontal coordinate system uses the observer's horizon.