A city modelled according to planning regulations usually presents a correlation between plots and building dimensions. To simulate the overall impact of building regulations over a large number of plots it is advantageous to use a computational tool to perform the task. Existing software can generate proxies of the would be reality, but do not accurately simulate the impact of alternative urban regulations. CityZoom is a Decision Support System for urban planning which not only provides CAD tools, but also allows users to evaluate and modify the city model according to different constraints such as solar radiation, luminance, terrain's pervious conditions, etc. By simulating specific urban regulations and addressing environmental comfort issues, CityZoom helps architects to simultaneously evaluate the different attributes of a particular design. Coupled with GIS tools, CityZoom allows users to perform multiple analyses over the existing database and use the resultant feedback to optimize proposed solutions. Future developments envisage giving CityZoom a more autonomous role, using artificial intelligence to optimize building shapes and dimensions.