It is a precision drawing, first drafted and then colored in. A geometric structure so it is spatially algorithmic - if I remember correctly, it was a trisected line with an extension at 30 degrees and a self similar grid can be obtained. This happens to be one instance of a possible tiling of the space. If you note, this panel has (discounting the border black blocks which would extend way out into a much larger surface) 3 degrees of recursion. The middle rectangle is identical to the overall image and also contains a tiny image of itself.