In the entire European Region over 80% of the adolescents are not active enough (WHO, 2019b). Physical activity can be seen as an essential component of human health as it can contribute to reducing the risk at several diseases, such as diabetes, depression, and several types of cancer (World Health Organization, 2010, p.10). Physical activity behaviour is influenced by a high variety of variables, ranging from personal variables to the physical environment. The composition of public spaces can facilitate or hinder adolescent physical activity behaviour. Although a lot of research has been done already and studies increasingly included the physical environment, research shows inconsistencies regarding similar variables (e.g. Ding, Sallis, Kerr, Lee, & Rosenberg, 2011). This makes it difficult to apply the knowledge in urban design practice. The objective of this thesis is to explore the role of urban design in contributing to increase activity levels of adolescents using quantitative statistics. Literature review is used to identify attributes of (adolescent) physical activity behaviour. From this review spatial attributes are selected to research the preferences of adolescents to visit public spaces for physical activity. A choice based conjoint analysis (CBCA) is used to estimate the relative importance of ten spatial attributes for adolescent physical activity in outdoor public space. To illustrate how such statistical method can be used to inform urban design a square in Westland, the Netherlands is selected as a test case to transform. Westland showed to be the least green municipality, and adolescents in Westlands appeared less active than the Dutch average. The attributes that showed significantly important from the survey were used to analyse and transform an existing public space. Choice based conjoint analysis can be a valuable method to use in urban research and design, as one can identify user preferences before actually transforming the physical environment. However it is important to carefully define and use the attributes for the analysis, and to avoid misinterpretation as much as possible. Choice based conjoint analysis can identify what spatial attributes are important and with that an urban designer can show how these can be implemented in urban design.