Environment and Planning II Planning and Design 1999, volume 26, pages 333 343 Structure of a planning support system for urban development L D Hopkins Department of Urban and Regional Planning, University of Illinois at Urbana-Champaign, Room i l l Temple Bucll Hall 611 Tafi Drive, Champaign, IL 61820-6921, USA; e-mail: L-Hopkins@uiuc.cdu Received 15 January 1998; in revised form IS September 1998 Abstract* The idea of a planning support system, if not the label, has been with us for at least twenty- five years. Many components have been developed but wc lack an underlying structure with which to integrate these components. GIS provide useful tools but the map concepts on which they are built are insufficient for a planning support system. The structure proposed here builds on elements of geographic modeling and of planning. It works with actors,flows,investments, facilities, regulations, and rights, as well as elements familiar in GIS. It includes views and tools for sketch planning, model building, scenario building, evaluation, lineage tracking, and plan-based action. 1 Planning support systems Designing computing tools to support planning is an old idea. The Chicago Area Transportation Study used computers to run its models and displayed some of its results as travel desire lines on a primitive cathode-ray tube in the 1950s (CATS, I960). Britton Harris (1960) has long argued for an approach to planning that combines sketch planning—rapid and partial description of alternatives—with state-of-the-art modeling of the implications of these alternatives. He has developed several highly refined computing tools for such modeling. Mel Branch (1971) described an elaborate planning support system for 'continuous city planning*, including the design of a room for collaboration with citizen boards. Most of the tasks we now imagine were included in his proposal, but computing was a minor medium for calculation and not for display or direct interaction. More recently, Harris and Mike Batty (1993) argued for coherent sets of tools for such tasks and labeled them planning support systems (PSS). They identify "... two principal requirements for planning, which devolve onto any planning support system. First, since optimization (which equates with the automatic generation of plan) is impossible, the search for good plans must be by way of an informed process of trial and error which generates alternatives and prepares them for testing. This is often called sketch planning. Second, planning and policy making need extensive tools for tracing out the consequences of alternatives, since otherwise there is no way to compare alterna- tives on the basis of their costs and benefits, and no way to look for means of improving or replacing alternatives" (pages 193 -194). New plans for Washington, DC (NCPC, 1997) and Madrid (Neuman, 1997) provide recent examples of sketches that were central in the development of plans. In the Portland 2040 planning process in Portland, Oregon, alternative development patterns were considered, initially in fairly abstract form equivalent to sketches, and then their consequences were traced out through the use of models. Portland area planners also monitor the effects of implementation tools relative to plan intentions and adjust actions to achieve intentions.