Editing Coordinate system (section)

==Coordinate lines/curves==
{{Anchor|Coordinate axis|Coordinate line|Coordinate curve}}
{{Redirect-distinguish|Coordinate line|Line coordinates}}

Given a coordinate system, if one of the coordinates of a point varies while the other coordinates are held constant, then the resulting curve is called a '''coordinate curve'''. If a coordinate curve is a [[straight line]], it is called a '''coordinate line'''. A coordinate system for which some coordinate curves are not lines is called a ''[[curvilinear coordinate system]]''.<ref>{{cite book |title=Mathematical Methods for Engineers and Scientists |volume=2|first=K. T.|last=Tang|publisher=Springer|year=2006|isbn=3-540-30268-9|page=13}}</ref>
''[[Orthogonal coordinates]]'' are a special but extremely common case of curvilinear coordinates.

A coordinate line with all other constant coordinates equal to zero is called a '''coordinate axis''', an [[oriented line]] used for assigning coordinates. 
In a [[Cartesian coordinate system]], all coordinates curves are lines, and, therefore, there are as many coordinate axes as coordinates. Moreover, the coordinate axes are pairwise [[orthogonal]]. 

A polar coordinate system is a curvilinear system where coordinate curves are lines or [[circle]]s. However, one of the coordinate curves is reduced to a single point, the origin, which is often viewed as a circle of radius zero. Similarly, spherical and cylindrical coordinate systems have coordinate curves that are lines, circles or circles of radius zero.

Many curves can occur as coordinate curves. For example, the coordinate curves of [[parabolic coordinates]] are [[parabola]]s.