Williamson, C.J.S. Mechanics of Zoning Adjustments. The Annals of the American Academy of Political and Social Science. May 1931, 155 (2): 108–122. S2CID 145796947. doi:10.1177/000271623115500215.
Hot Spots 2013. nicb.org. [October 23, 2014]. (原始内容存档于2017-09-13).
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Williamson, C.J.S. Mechanics of Zoning Adjustments. The Annals of the American Academy of Political and Social Science. May 1931, 155 (2): 108–122. S2CID 145796947. doi:10.1177/000271623115500215.