Urban planners are usually hired by developers, private property owners, private planning firms and local/regional governments to assist in the large-scale planning of communal and commercial developments, as well as public facilities and transportation systems. Urban planners in the public role often assist the public and serve as valued technical advisors in the myriad web of the community’s political environment. Related disciplines include regional, city, environmental, transportation, housing and community planning.

Source: Wikipedia

Urban design theory deals primarily with the design and management of public space (i.e. the ‘public environment’, ‘public realm’ or ‘public domain’), and the way public places are experienced and used. Public space includes the totality of spaces used freely on a day-to-day basis by the general public, such as streets, plazas, parks and public infrastructure.

Some aspects of privately owned spaces, such as building facades or domestic gardens, also contribute to public space and are therefore also considered by Urban design theory. Important writers on, and advocates for, urban design theory include Christopher Alexander, Michael E. Arth, Edmund Bacon, Peter Calthorpe, Gordon Cullen, Andres Duany, Jane Jacobs, Jan Gehl, Kevin Lynch, Roger Montgomery, Aldo Rossi, Colin Rowe, Robert Venturi, William H. Whyte, Bill Hillier, and Elizabeth Plater-Zyberk.

While the two fields are closely related, ‘urban design’ differs from ‘urban planning’ in its focus on physical improvement of the public environment, whereas the latter tends, in practice, to focus on the management of private development through planning schemes and other statutory development controls.

Source: Wikipedia