Cities are constantly evolving: buildings are built and demolished, altering the landscape of our cities; Urban Plans describe what we want our cities to be, undergoing revisions as we change our vision of the future of our cities. This paper presents a methodology to model the interactions between what the city is and what it wants to become. The old quarter of Sant Andreu in Barcelona (Spain) was used in a pilot study for the development of a methodology to automatically quantify and visualize the outcome of regulation changes as a strategic tool for the Urban Planning Department of the Barcelona City Council. This paper describes a methodology developed to measure the magnitude of the buildings conformity or disconformity to the determinations of the Urban Plan (current and proposed), and to display this information in 3D, to allow a more natural interpretation of the results. Special care was put into the methodological approach to ensure that it could be replicated at neighbourhood or city-wide scales. A methodology for the interpretation of the heights of staircase towers and ventilation courtyards from neighbouring entities heights, through the analysis of adjacency relationships in a non-topological Geographic Information System is also discussed.