Planning theory is the body of scientific concepts, definitions, behavioral relationships, and assumptions that define the body of knowledge of urban planning. There are nine procedural theories of planning that remain the principal theories of planning procedure today: the Rational-Comprehensive approach, the Incremental approach, the Transformative Incremental (TI) approach, the Transactive approach, the Communicative approach, the Advocacy approach, the Equity approach, the Radical approach, and the Humanist or Phenomenological approach. Background Urban planning can include urban renewal, by adapting urban planning methods to existing cities suffering from decline. Alternatively, it can concern the massive challenges associated with urban growth, particularly in the Global South. All in all, urban planning exists in various forms and addresses many different issues. The modern origins of urban planning lie in the movement for urban reform that arose as a reaction against the disorder of the industrial city in the mid-19th century. Many of the early influencers were inspired by anarchism, which was popular in the turn of the 19th and 20th centuries. The new imagined urban form was meant to go hand-in-hand with a new society, based upon voluntary co-operation within self-governing communities. In the late 20th century, the term sustainable development has come to represent an ideal outcome in the sum of all planning goals. Sustainable architecture involves renewable materials and energy sources and is increasing in importance as an environmentally friendly solution Blueprint planning Since at least the Renaissance and the Age of Enlightenment, urban planning had generally been assumed to be the physical planning and design of human communities. Therefore, it was seen as related to architecture and civil engineering, and thereby to be carried out by such experts. This kind of planning was physicalist and design-orientated, and involved the production of masterplans and blueprints which would show precisely what the 'end-state' of land use should be, similar to architectural and engineering plans. Similarly, the theory of urban planning was mainly interested in visionary planning and design which would demonstrate how the ideal city should be organised spatially. Sanitary movement Although it can be seen as an extension of the sort of civic pragmatism seen in Oglethorpe's plan for Savannah or William Penn's plan for Philadelphia, the roots of the rational planning movement lie in Britain's Sanitary movement (1800–1890). During this period, advocates such as Charles Booth argued for central organized, top-down solutions to the problems of industrializing cities. In keeping