Any scheme for the unique identification of each point of a given continuum. These may be points in space (Eulerian coordinates) or parcels of a moving fluid (Lagrangian coordinates). Newton's laws of motion do take different forms in different systems (see inertial coordinate system, relative coordinate system). The geometry of the system is a matter of convenience determined by the boundaries of the continuum or by other considerations (see Cartesian coordinates, curvilinear coordinates).