The criterion for finding the best path is specified by the user in terms of the way the feature appears in the image. The image may be preprocessed in advance to enhance the appearance of the feature before digitisation. If the algorithm fails to find a suitable path for a segment, that segment can be digitised manually as a series of straight lines.
A disadvantage of this approach is that only single segments can be digitised. If there are junctions, such as river tributaries, then these must be digitised separately and no information is kept about the junction.