8Alperovich G. 1992, Economic Development and Population Concentration, Economic Development and Cultural Change, 41, pp. 63-74.
9Ottaviano G I P, Puga D, 1998, Agglomeration in the Global Economy. A Survey of the New Economic Geography, World Economy,Vol. 21, Issue 6, pp 707-731.
10Paluzie E, Pore J, and Tirado D A. 2001, Regional Integration and Specialization Patterns in Spain, Regional Studies. Vol 35. 4pp. 285-296.