logic is of course that noise and other small variations are unlikely to result in a strong edge
(with proper adjustment of the threshold levels). Thus strong edges will (almost) only be due to
true edges in the original image. The weak edges can either be due to true edges or noise/color
variations. The latter type will probably be distributed independently of edges on the entire
image, and thus only a small amount will be located adjacent to strong edges. Weak edges due
to true edges are much more likely to be connected directly to strong edges.