Context theory is the theory of how environmental design and planning of new development should relate to its project. When decisions have been made they are implemented by means of land Use plans, zoning plans and environmental assessments. A number of context theories set out principles for relationships new designs and the existing environment.
Picturesque theorists argued that landscapes should be composed 'like a picture' (i.e. a landscape painting) with a foreground, a middle ground and a background. The theory was applied to landscape gardens in the eighteenth century and, as Nikolaus Pevsner argued, to the wider topic of regional planning in the twentieth century. This produced the context theory that towns (the foreground) should be compact and urban, that the surrounding countryside (the middle ground) should retain its agricultural character and that remote areas (the background) should remain as natural parks.
Modernist town planners lacked sympathy with picturesque context theory. Their firm belief that 'form follows function' led to the prioritising of certain human needs over environmental considerations or deeper issues of meaning. When planning a new road, for example, the emphasis was on traffic analysis and engineering rather than on the relationship between the new road and its environmental context.
Ian McHarg opposed Modernist planning in his book Design with Nature. He believed that new development should be preceded by the fullest possible analysis of the environmental context in which building would take place. The highway planners who were, in his view, destroying the American landscape at that time were described as 'highwaymen'.
Kenneth Frampton put forward a context theory which he described as Critical Regionalism to help consider the relationship between new architecture and its context. He believed that designers should make a critical response, rather than a sentimental or copyist response, to local design traditions.
Tom Turner, in chapter 3 of a book on Landscape Planning and Environmental Impact Design (1998), argued for a broad approach to context theory based on an index of Similarity, Identity and Difference (the SID Index): "On different occasions... a powerful case can be made for developments which are 'similar to', 'identical with' or 'different from' their surroundings." (p.88)
Jonathan Watts reported (on Tuesday June 12, 2007 in The Guardian), "China has become the land of 1,000 identical cities, a senior government official has warned in an outspoken attack on the country's rush towards modernity."