1. Alonso, W.,The System of Intermetropolitan Population Flows, Institute of Urban and Regional Development, Working Paper No. 155, University of California, Berkeley, 1971.
2. Alonso, W. and E. Medrich,Spontaneous Growth Centers in Twentieth Century American Urbanization, Center for Planning and Development Research, Working Paper No. 113, Institute for Urban and Regional Development, University of California, Berkeley, 1970.
3. Beale, C. L., ?Rural Development: Population and Settlement Prospects,?Journal of Soil and Water Conservation, Vol. 29, No. 1, 1974, pp. 23?27.
4. Garrison, W. L. and D. F. Marble, ?Factor Analytic Study of the Connectivity of a Transportation System,?Proceedings Regional Science Association, Vol. 12, 1963, pp. 231?239.
5. Goddard, J. B., ?Functional Regions Within the City Center,?Transactions Institute of British Geographers, No. 49, March 1970, pp. 161?182.