1. A tracking structure comprising: a two-dimensional substantially planar mat which incorporates a first plurality of conductive elements, members of the first plurality extend linearly, spaced apart from one another, across the mat generally in a first direction and a second plurality of conductive elements, members of the second plurality extend linearly, spaced apart from one another across the mat generally in a second direction; and at least one wireless identification unit, which when located adjacent to a region of the mat induces an electrical signal in at least one member of each plurality.