A surface such as a

*plane*or the surface of a cylinder or*sphere*has a dimension of two because two coordinates are needed to specify a*point*on itfor example, both a latitude and longitude are required to locate a*point*on the surface of a*sphere*. The inside of a cube, a cylinder or a*sphere*is*three*-*dimensional*because three coordinates are needed to locate a*point*within these*spaces*. In classical mechanics,*space*and time are different categories and refer to absolute*space*and time. That conception of the world is a four-dimensional*space*but not the one that was found necessary to describe electromagnetism.