1. Faculty of Geography, Philipps-University of Marburg, Deutschhausstraße 10, D-35032 Marburg, Germany
2. Department of Social and Economic Geography, and Centre for Research on Innovation and Industrial Dynamics (CIND), Uppsala University, PO Box 513, S-751 20 Uppsala, Sweden
3. Danish Research Unit for Industrial Dynamics (DRUID), Department of Industrial Economics and Strategy (IVS), Copenhagen Business School (CBS), Howitzvej 60, DK-2000 Frederiksberg, Denmark