Park systems can significantly improve public health by influencing key determinants like physical activity, air quality, and access to nature. The document discusses case studies of park system plans in Cleveland, Prince George's County, and Philadelphia that aim to maximize these public health benefits. The Cleveland plan focuses on connecting urban parks and restoring ecosystems. The Prince George's plan partners with health organizations to reduce obesity and disease through trails, programs, and policy. Philadelphia's plan expands the definition of open space to more components of the urban fabric.