Robert talks of the grids in his 1st edition of Astral Dynamics.
He describes the surface of an astral plane as two dimensional and covered with perfectly straight horizontal and vertical grid lines, making for a checkered appearance over the entire surface.Each square on a surface contains a brilliantly multicoloured geometric design repeated endlessly in all the squares.
He even describes the connection between each plane being made by colour. His back cover displays this.
I'd forgotten just how seriously good this book is.