E. J. Cilliers,  The Urban Development Boundary as a Planning Tool for Sustainable Urban Form: The South African Situation.   journal   = {International Journal of Humanities and Social Sciences}, [online]. World Academy of Science, Engineering and Technology.
    June 2009, vol. 30(6). 942 - 947
    [viewed 17 January 2020]. Available from: https://publications.waset.org/pdf/12075.