Online Encyclopedia
Coordinate system
See Cartesian coordinate system or Coordinates (elementary mathematics) for a more elementary introduction to this topic.
In mathematics as applied to geometry, physics or engineering, a coordinate system is a system for assigning a tuple of scalars to each point in an ndimensional space. "Scalars" in many cases means real numbers, but, depending on context, can mean complex numbers or elements of some other field. More generally, coordinates may sometimes be taken from rings or other ringlike algebraic structures.
Although any specific coordinate system is useful for numerical calculations in a given space, the space itself is considered to exist independently of any particular choice of coordinates. By convention the origin of the coordinate system in Cartesian coordinates is the point (0,0,...,0), which may be assigned to any given point of Euclidean space. Other coordinate systems do not, however, have a clear notion of origin. For example polar coordinates (r,θ) assign the point (x,y) = (0,0) the value r = 0 but θ any angle.
Contents 
Examples
An example of a coordinate system is to describe a point P in the Euclidean space R^{n} by an ntuple
 P = (r_{1},...,r_{n})
of real numbers
 r_{1},...,r_{n}.
These numbers r_{1},...,r_{n} are called the coordinates of the point P.
If a subset S of a Euclidean space is mapped continuously onto another topological space, this defines coordinates in the image of S. That can be called a parametrization of the image, since it assigns numbers to points. That correspondence is unique only if the mapping is bijective.
The system of assigning longitude and latitude to geographical locations is a coordinate system. In this case the parametrization fails to be unique at the north and south poles.
Transformations
A coordinate transformation is a conversion from one system to another, to describe the same space.
Some choices of coordinate systems may lead to paradoxes, for example, close to a black hole, but can be understood by changing the choice of coordinate system. At an actual mathematical singularity the coordinate system breaks down.
Systems commonly used
Some coordinate systems are the following:
 The Cartesian coordinate system (also called the "rectangular coordinate system"), which, for threedimensional flat space, uses three numbers representing distances.
 For any finitedimensional vector space and any basis, the coefficients of the basis vectors can be used as coordinates. Changing the basis is a coordinate transformation, a linear transformation that can be summarized by a matrix, and is computationally the same as a mapping of points to other points keeping the bases the same: e.g. in 2D:
 a clockwise rotation is a mapping of points to other points which changes the coordinates the same as keeping the points in place but rotating the coordinate axes anticlockwise. The rotation of coordinate systems http://en.wikibooks.org/wiki/Modern_Physics:Math:Vectors is covered in depth on wikibooks.
 an expansion by a factor two in the direction of one basis vector is a mapping of points to other points which changes the coordinates the same as keeping the points in place but halving the magnitude of that basis vector (in both cases the corresponding coordinate is doubled).
 a mapping of points to other points which distorts a rectangle to a parallelogram changes the coordinates the same as keeping the points in place but changing the basis vectors from being two sides of that parallellogram to perpendicular ones, two sides of that rectangle.
 Curvilinear coordinates are a generalization of coordinate systems generally; the system is based on the intersection of curves.
 The polar coordinate systems
 Cylindrical coordinate system represents a point in space by an angle, a distance from the origin and a height.
 Spherical coordinate system represents a point in space with two angles and a distance from the origin.
 Generalized coordinates are used in the Lagrangian treatment of mechanics
Astronomical systems

Celestial coordinate system
 Horizontal coordinate system
 Equatorial coordinate system  based on Earth rotation
 Ecliptic coordinate system  based on Solar System rotation
 Galactic coordinate system  based on Milky Way rotation

extragalactic coordinate systems
 supergalactic coordinate system  based on plane of local supercluster of galaxies
 comoving coordinates  valid to particle horizon
 Binary coordinate system
External links
 Capětal city coordinates http://times.clari.net.au/index.htm