Efficient Decision Support Systems -Practice and Challenges From Current to Future 460 general shape of the territory (at the urban or regional scale), planners have to access to specific models and data processing systems with friendly user interface, while it is not essential to have very detailed and precise outputs. In other words, at the beginning of planning process it is important to have the order of magnitude of a complete variety of phenomena, which in the following phases can be

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... eted in an exhaustive way. Urban planning and location problems Urban planning is the instrument to improve the best distribution of human activity on the territory (Benevolo, 1963). Planners developed localisation theory at the same time with the analysis of urban models since the mono-centre scheme deepened by Von Thünen (1826). His model of land use, that connected market processes and land use, was based on the assumption of maximizing the profits by the actors (farmers). Localisation was closely connected to the physical distance among different land uses. This deterministic and static concept took its stands on the principle of equilibrium status. As a simplified scheme, it was related to a specific problem, and localisation itself must be considered as a particular theme into a wide-ranging and integrated model. However, at the urban scale, localisation theory always referred to the most relevant topics that strongly characterized the growth of the cities: first the agriculture land use, then the industrial areas and the big residential districts, until the commercial facilities and the distribution of urban public services (the service-oriented city). Until 1954, general localisation theory has been related to a specific geometrical scheme (MacKinder in 1902 and Weber in 1909, which Christaller developed in his Central Place Theory in 1933), always in relation to new cities addressed to industrial settings, showing a restricted application domain. In 1954 Mitchel and Rapkin put in rigid connection land use and urban traffic also considering the modal split; this idea was used in the transportation plans of Chicago and Detroit, showing its practical use in city planning. The Gravity Model by Lowry and Garin (developed in 1963), applied in Pittsburgh, offered a new understanding both in the field of a general urban model and in the definition of two sub-models regarding economic topics and localisation (assigning to this last theme a specific role). Even considering Von Neumann's and Morgenstern's criticism of the rational research of optimal solutions with the introducing of the concept of sub-optimal, urban models concerning location like problems spread in the last 40 years in many real contexts at urban and regional scale. It is important not to merge localisation models with Operational Large Scale Urban Models (OLSUMs) that are mathematical simulation models describing comprehensive urban systems in great details (spatial, with a fine zoning of the territory, and functional, with a disaggregated account of urban activities and infrastructures) 1 . Localisation and accessibility in consolidated or historical cities Application of location and accessibility models to real contexts implies the definition of the invariant conditions: consolidated and historical cities can not be warped with new mobility 1 Born in USA late '50s of the last century, these models flourishes at best in '60s and '70s, especially in UK in a large number of applications for sub-regional territorial planning. The critics of Lee in 1973, in his very famous paper "Requiem for large-scale models", helped the lost of interest in '80s and '90s. Since the end of the XX century a slow but growing interest can be remarked.