At a given location, a full representation of the Earth's magnetic field requires a vector with three coordinates (see figure). These can be Cartesian (North, East and Down) or spherical (declination, inclination and intensity). In the latter system, the declination (the deviation from true north, a horizontal angle) must be measured first to establish the direction of magnetic North; then the dip (a vertical angle) can be measured relative to magnetic North.[6] In China, the horizontal direction was measured as early as the fourth century BC, and the existence of declination first recognized in 1088.