1. Department of Science, International Cooperation and Library , University of Agriculture and Forestry, Hue University , 102 Phung Hung , Hue City , Vietnam
2. Department of Human Geography and Spatial Planning , Utrecht University , Princetonlaan 8a, 3584 CB Utrecht , The Netherlands
3. Department of Geography , National Taiwan Normal University , 162, Section 1, Heping E. Rd., Taipei City 106, Taiwan