A range of numbers, allows the position of features to be interpolated to much greater degree of accuracy. Movements by a point away from the axes are recorded as a set of two values, known as coordinates. By convention, the point's position is identified by quoting the distance along the X axis first, and distance along the Y axis second, thus each point has a unique name. These are the mathematical coordinates you find on a map. In cartography and surveying, the X axis coordinates are known as Eastings, and the Y axis coordinates as Northings.
Cartesian Coordinates can define a point in space, that is, in three dimensions.
To do this, another axis must be introduced. This axis will represent a height above the surface defined by the x and y axes. This new axis is known as the Z axis. This diagram shows the earth with two local coordinate systems defined on either side of the earth. The Z axis points directly up into the sky.