This is simple: the first line is the location of the grid's center point in the world (coordinates), and the second line is the angle where grid faces in.
14.5 , -0.05 , 52 // Location of the grid
270 // Angle, where grid faces in.
Some help for choosing the angle: (horizontally mirrored compass)
0 = 360 = North
45 = NorthWest
90 = West
180 = South
270 = East
And so on. If you place the grid on a slope, some of the cars might be partially "sinked" to the ground, and then they can't move when the countdown finishes.
The network starting points are defined similarly. The network start points are also used for explicit opponents. (Defined in data/races.txt)