In our research, we grouped the LULC types into seven categories: (1) high-impervious surface (, high-density urban, including CBD, roads, squares, and so on), (2) medium-impervious surface (50 to 90%, high-density residential land), (3) low-impervious surface (, low-density residential land), (4) arable land (agricultural land), (5) forest land, (6) bare land, and (7) water body. Because we focused on urbanization, only urban-related classes, including high-/medium-/low-impervious surfaces, were utilized for accuracy assessment. Sun et al. proved that the estimation accuracy of impervious surfaces was superior to Landsat TM/ETM+ imagery (acquired on June 3, 2009) using an SVM method.30 Figures 5 and 6 illustrated the percentages and spatial distributions of LULC classes in the Beijing region from 1992 to 2009. Forest and arable lands dominated in the whole area but decreased with the continuous increase of urban areas, especially agricultural land. The urbanization level (high-impervious surface), the proportion of urbanized area to the total land area, was 4.28, 6.03, 8.34, and 12.78% in 1992, 1999, 2006, and 2009, respectively. The proportion of residential area to the total land area was 3.21, 3.15, 3.83, and 6.66% in 1992, 1999, 2006, and 2009, respectively. Urban areas increased from 4.28% in 1992 to 12.78% in 2009, and residential areas increased from 3.21% in 1992 to 6.66% in 2009, while agricultural land areas decreased from 27.20% in 1992 to 11.44% in 2009.