As a design medium, collage has significant conceptual implications. It compares with photomontage but generally works in plan. The word 'collage' comes from the verb 'to glue' and is associated with the asssmbly of different types of material (newsprint, fabrics, photographs etc) by Braque and Picasso.
The placing of patch upon patch implies a build-up of layers. They can be chronological, biological, territorial, functional or something else. Natural landscape often has a collage aspect: water meets land; mountain meets plain; forest meets savannah; oasis meets desert. Town maps have some of these conjugations and others that relate to the functional patterns of human settlements: nineteenth century housing meets twentieth century housing; industry meets housing; housing meets school. As land has always developed in this way, there is much to be said for a design approach that employs collage instead of pen-drawing. Colin Rowe argued along these lines in Collage City (Rowe, 1978). The book has inspiring illustrations but the text is impenetrable.