The study of the way in which the pattern of streams in a drainage basin is organized. Classical work focused on the relations between the components of a network, e.g. on the link between the importance (or ‘order’) of a stream segment and its frequency. Certain ‘laws’ of drainage network composition were derived. The modern approach emphasizes the importance of random processes in an explanation of these ‘laws’ and is more concerned with the density of the drainage network (drainage density = total length of channels/drainage area).