Sets the aspect ratio (drawing height/drawing width) for the drawing. Note that
this is adjusted before the size attribute constraints are
enforced. If ratio is numeric, it is taken as the desired aspect ratio. Then, if the
actual aspect ratio is less than the desired ratio, the drawing height is scaled up to achieve
the desired ratio; if the actual ratio is greater than that desired ratio, the drawing width
is scaled up. If ratio = "fill" and the size attribute is set,
the drawing is scaled to achieve the aspect ratio implied by size. As size is set, when the
drawing is later scaled to fit that rectangle, the resulting picture will fill the rectangle.
If ratio = "compress" and the size attribute is set, dot attempts
to compress the initial layout to fit in the given size. This achieves a tighter packing of
nodes but reduces the balance and symmetry.