of the Sheldonian. Christ Church Cathedral uniquely serves as both a college chapel and as a cathedral. In 2012–2013, the university built the controversial one-hectare (400 m × 25 m) Castle Mill development of 4–5-storey blocks of student flats overlooking Cripley Meadow and the historic Port Meadow, blocking views of the spires in the city centre. The development has been likened to building a "skyscraper beside Stonehenge". Parks The University Parks are a 70-acre (28 ha) parkland area in the northeast of the city, near Keble College, Somerville College and Lady Margaret Hall. It is open to the public during daylight hours. As well as providing gardens and exotic plants, the Parks contains numerous sports fields, used for official and unofficial fixtures, and also contains sites of special interest including the Genetic Garden, an experimental garden to elucidate and investigate evolutionary processes. The Botanic Garden on the High Street is the oldest botanic garden in the UK. It contains over 8,000 different plant species on . It is one of the most diverse yet compact major collections of plants in the world and includes representatives of over 90% of the higher plant families. The Harcourt Arboretum is a site south of the city that includes native woodland and of meadow. The Wytham Woods are owned by the university and used for research in zoology and climate change. There are also various collegiate-owned open spaces open to the public, including Bagley Wood and most notably Christ Church Meadow. Organisation As a collegiate university, Oxford is structured as a federation, comprising over forty self-governing colleges and halls, along with a central administration headed by the Vice-Chancellor. Academic departments are located centrally within the structure of the federation; they are not affiliated with any particular college. Departments provide facilities for teaching and research, determine the syllabi and guidelines for the teaching of students, perform research, and deliver lectures and seminars. Colleges arrange the tutorial teaching for their undergraduates, and the members of an academic department are spread around many colleges. Though certain colleges do have subject alignments (e.g., Nuffield College as a centre for the social sciences), these are exceptions, and most colleges will have a broad mix of academics and students from a diverse range of subjects. Facilities such as libraries are provided on all these levels: by the central university (the Bodleian), by the departments (individual departmental libraries, such as the