The red plastic cover fits over the base to protect the internal cables and antenna elements and provide a ramped edge to the mat. The underside of the cover includes the Snap-In Buttons which fit in to the black plastic base, and the guide joints additionally slot in to the base. 

The cover is symmetrical and the orientation of installation does not matter. 

The edges of the cover are designed to flex when setup to provide a smooth transition from the ground. Additionally on the underside of the edges is an additional groove which can be used to run additional cables such as power cables or Active Loop Cables.