This pedagogical paper presents an approach to urban design taught in the "Complex Densities Studio" CDS of the Institute of Architecture and Earth Sciences of Setif (IAST). This approach is based on urban analysis and scenario building, the use of parametric tools, and the constitution of reusable "parametric actions". The parametric approach invites students to state their project intentions. Parametric computing allows building a digital model from certain parameters. The digital model aims to verify the interactions of the student project in the urban context dynamically and iteratively. It offers the possibility of identifying the most efficient models concerning the stated criteria. The urban typologies and ambiances are evaluated throughout the design process, thus allowing for permanent adjustments. The chosen context is the El-Harrach district in the city of Algiers: the population density and the rapid transformation of urban areas offer a stimulating framework to experiment with a parametric approach to the student project. The approach of the CDS is based on numerous and diverse data, transcribed in diagrams, pre-formal plans, and parametric models, allowing to move from an abstract and quantitative dimension to the formalization of urban ambiances in a progressive and qualitative way.