Longitude and latitude

Longitude

Longitude is the angular distance of a point's meridian from the Prime (Greenwich) Meridian. It is usually expressed in degrees, minutes, and seconds. Lines of longitude are often referred to as meridians , identified by the Greek letter lamba lambda (λ), is the geograpic coordinate most commonly used in cartography and global navigation for east-west measurement. Constant longitude is represented by lines running from north to south. The line of longitude (meridian) that passes through the Royal Observatory, Greenwich, in England, establishes the meaning of zero degrees of longitude, or the Prime Meridian. Any other longitude is identified by the east-west angle, referenced to the center of the Earth as vertex, between the intersections with the Equator of the meridian through the location in question and the Prime Meridian. A location's position along a meridian is given by its latitude, which is identified by the north-south angle between the local vertical and theplane of the Equator.

Latitude

Latitude, usually denoted by the Greek letter phi (φ) gives the location of a place on Earth (or other planetary body) north or south of the equator. Lines of Latitude are the imaginary horizontal lines shown running east-to-west (or west to east) on maps (particularly so in the Mercator projection) that run either north or south of the equator. Technically, latitude is an angular measurement in degrees (marked with °) ranging from 0° at the equator (low latitude) to 90° at the poles (90° N or +90° for the North Pole and 90° S or −90° for the South Pole). The latitude is approximately the angle between straight up at the surface (the zenith) and the noonday sun when it is at the equinox. The complementary angle of a latitude is called the colatitude.
All locations of a given latitude are collectively referred to as a circle of latitude or line of latitude or parallel, because they are coplanar, and all such planes are parallel to the equator. Lines of latitude other than the Equator are approximately small circles on the surface of the Earth; they are not geodesics since the shortest route between two points at the same latitude is a path that (when drawn on most small-scale maps) seems to bulge toward the nearest pole, first moving farther away from and then back toward the equator (see great circle).