Relational dimensions of regional growth : introduction to the Special Issue - Suau-Sanchez, Pere (Cranfield University. Department of Air Transport) ; Pallares-Barbera, Montserrat (Universitat Autònoma de Barcelona. Departament de Geografia) ; Tamásy, Christine (University of Vechta. Institute for Spatial Analysis and Planning) ; Taylor, Mike (University of Birmingham. School of Geography, Earth and Environmental Sciences)