To test this proposition, the regional centrality indices for Manila and Bangkok were recalculated using a new hub-specific region for each city (Fig. 8).
Each new region was defined as the area contained within a radius of 1600 miles (2575 km) ± a distance similar to that which defines the extent of Southeast Asia from Singapore. A complete set of 1997 gateway cities for each new region was determined and Shimbel indices were computed. The results indicate that redefining the region of each hub did produce a slight increase in the centrality of Bangkok, Jakarta, and Manila but Singapore continued to have a much higher level of intraregional centrality than its rivals (Table 7).