A coordinate system that is relative to the size and position of the layer, regardless of the project resolution. In this coordinate system, the point 0,0 is in the middle of the layer. Units on all axes are 1/100 of the layer height, so an x coordinate of -50 would be the left side of the layer, and an x coordinate of 50 would be the right side of the layer.
When used in three dimensions, an additional z coordinate is used. Here, zero is the viewport plane (the camera) and positive values move away from the camera, into the screen. When using this coordinate system to measure sizes, keep in mind that a height of 100, although equal to the layer height, may appear smaller of an object is placed away from the camera.