Before revision: Exurbs can be defined in terms of population density across the extended urban area, for example "the urban core (old urban areas including Siming and Huli, where the population density is greater than 51 persons per ha), the suburban zone (old urban and new urban transitional zones including Haicang and Jimei, where the population density is greater than 8 persons per ha), and the exurban areas (newly urbanized areas including Tong'an and Xiang'an, where the population density is less than 8 persons per ha)".
After revision: Exurbs can be defined in terms of population density across the extended urban area, for the example of Xiamen "the urban core (old urban areas including Siming and Huli, where the population density is greater than 51 persons per ha), the suburban zone (old urban and new urban transitional zones including Haicang and Jimei, where the population density is greater than 8 persons per ha), and the exurban areas (newly urbanized areas including Tong'an and Xiang'an, where the population density is less than 8 persons per ha)".