6Green F H W. Urban hinterlands in England and Wales: An analysis of bus services. Geogr. J., 1950,96 (1):64-81
7Goddard J B. Functional regions within a city center: A study by factor analysis of taxi flows in Central London. Trans. Inst. Br. Geogr., 1970,49(2) :161-180.
8Edward J Taffe. The urban hierarchy: An air passenger definition. Economic Geography, 19 6 2,3 7 (1) : 1- 14.
9Garrison W L. Spatial structure of economy I . Annals of the Association of American Geographers, 1959,49:238 -239.
10Garrison W L, Spatial structure of economy Ⅱ. Annals of the Association of American Geographers, 1959,49:471-482.
