## 2 Study Area and Data Sources  
### Study Area  
Chongqing (Figure 1) is located in southwest China (105 deg17\" E-110 deg11' E, 28 deg10' N-32 deg13' N), and the total basin area is approximately 82,400 km\({}^{2}\), extending 450 km from the north to south and 470 km from the east to west. It is an important strategic fulcrum city for the development of the western region [20], construction of the \"Belt and Road,\" and development of the Yangtze River Economic Belt. The study area is located in the northwestern part of the main city of Chongqing, covering nine districts. Located between Huaying Mountain and Fangdou Mountain, it is located in the low hilly area of the parallel ridge valley. The terrain is high in the north and low in the south, west, and east. The Jialing River flows from the north to south, cutting through the three anticline mountains of Yunwu Mountain, Jinyun Mountain, and Zhongliang Mountain. When the mountains are cut down in the folds, valleys are formed crossing the mountains. The terrain is both high and low, and the maximum height difference is approximately 820 m. The study area [21] experiences mild climate, abundant rainfall, cloudy, scanty sunlight, and high humidity. The annual average temperature is 18.5 degC, annual precipitation approximately 1114.6 mm, and average annual sunshine time 1254.5 h; furthermore, in the areas belonging to the low-sunshine area, the annual number of cloudy days is as many as 204 days.  
The study area has a variety of landforms, mainly mountainous; there are five types of landforms, namely, medium, low mountains, hills, platforms, and peace dams. The mountainous area (medium and low mountains) covers the area of 62,400 km\({}^{2}\), accounting for 75.8% of the total area; the hilly area is approximately 15,000 km\({}^{2}\), accounting for 18.2% of the total area; the platform and peace-dam area is 4900 km\({}^{2}\), accounting for 6% of the total area. Furthermore, the karst landforms are widely distributed, and they are characterized by \"one mountain, three ridges, and two troughs,\" which has become a unique type of land karst in Chongqing. The main types of land on the basis of use are classified as farm land, forest land, waters, building, grass, and shrubs, where the vegetation mainly consists of evergreen broad-leaved forests, secondary coniferous-leaves forests, bamboo forests, and evergreen broad-leaved shrubs.  
Supplemented by the vegetation community survey method, we conducted field surveys in May 2017. The route was laid according to the terrain and land cover types in the study area. The plots were mainly set up to have a more uniform spatial distribution of features and regional heterogeneity. In the survey, one to three samples of 5 m \(\times\) 5 m are selected at uniform locations of land cover with intervals of 5 to 10 km. The hand-held GPS is used to record the latitude and longitude coordinates, elevation, land cover type, and surface features. After removing some abnormalities from the sample points, a total of 284 survey samples were recorded. As a typical ecologically fragile area, Chongqing has complicated topography and landforms, various land cover types, and covers most of the Three Gorges Reservoir, highlighting its important ecological geographical location, so it is important to study the land cover classification of this area.