The Track Graph object can be used to map the length and height of any 3d spline, to a 2d graph spline. this can then be used with sweep-nurbs, or extrude-nurbs to visualize a track in 2D
the track graph object does not need to be inserted under any other object, and is independent of object hierarchy.
You need to link it to a spline.
lets make a track graph of the following GPX track.
to visualize this, you want to polygonize it, by inserting it under a nurbs, or sweep object.
Using nurbs and sweep, you can easily render this spline based 2D graph.