Background. There is growing interest in conceptualising public health problems such as physical inactivity as the outcome of multiple interacting factors within complex systems. Methods. We worked with stakeholders involved in a city-wide physical activity promotion programme in Derby, UK to prodiuce conceptual maps of the major modifiable drivers of physical activity, and used them to explore ways in which the existing programme took a systems approach, and how it might be enhanced. Semi-structured interviews were subsequently undertaken to assess their views on the contribution of the mapping approach. Results. Feedback from stakeholders described the mapping as valuable, especially in helping to identify the limitations of the original approach taken in the city. Conclusions. Even a very simple application of systems thinking can be a useful tool for disaggregating the key factors driving a system, helping to identify areas that merit greater attention, and supporting effective action.