“…The series of units UCA, CSA, RTA, RVA and UVA has the urban-rural gradient feature with gradient variation of several important characteristics of different administrative divisions, such as population density, average daily traffic, total energy consumption, street cleaning method and frequency. In general, population density, traffic density, energy consumption, and frequency of sweeping decreased along the urban-rural gradient, as shown in Table 1 (Zhao and Li, 2013). Additionally, UCA and CSA have relatively smooth and less damaged impervious surfaces, and regularly daily mechanical sweeping; RTA, RVA and UVA have heavily damaged imperious surfaces, and rarely street sweeping.…”