## 2 Materials and Methods
### CLQ Evaluation Method
#### 2.2.2 Indicator Selection  
Based on the proposed definition of CLQ, eight indicators were selected by integrating multi-source remote sensing data to construct a comprehensive CLQ indicator system (Table 1). The indicators used to evaluate soil fertility are soil fertility size and stability. Soil fertility size represents whether the current soil fertility is good, while soil fertility stability focuses on the state of soil fertility over a period of time. Soil fertility is affected by many factors, but the growth status of the vegetation can be used as a direct reflection of soil fertility [47]. Normalized Difference Vegetation Index (NDVI) is obtained from remote sensing images and can accurately reflect the growth of vegetation; thus, it is often referred to as the \"soil fertility index\" and has been used to fully characterize the soil fertility of cultivated land [37; 48]. In this study, we used the mean of NDVI and coefficient of variation (CV) of NDVI of cultivated land for three consecutive years to characterize the size and stability  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  
of soil fertility, respectively. For soil fertility size, we first calculated the average NDVI within one year and then calculated the average NDVI for three consecutive years. Due to weather conditions, high-quality remote sensing images (cloud cover was less than 10%) within one year were concentrated from September-November. September-November is a critical period for crop growth and harvesting in Guangzhou [49]. Therefore, the average NDVI during this period can effectively characterize the soil fertility of cultivated land. If the mean of NDVI is larger and the CV of NDVI is smaller for three consecutive years, then the soil fertility of cultivated land is better. To evaluate the natural conditions of the cultivated land, we chose the slope and topsoil texture, which are the most frequently used and representative indicators due to their wide availability [50; 51]. Previous studies have found that the slope is closely related to CLQ; that is, the greater the slope, the worse the CLQ [30]. Moreover, topsoil texture (0-30 cm) is most relevant to soil quality and crop growth, which is widely used in many previous CLQ evaluation studies [11; 40]. If the slope is smaller and the topsoil texture is fine, then the natural conditions of the cultivated land are better. To facilitate field production activities and meet the needs of agricultural mechanized production, farmers usually build a sound field road system and carry out land consolidation projects [19]. Therefore, in this study, road accessibility and centralized connectivity were used to represent the construction level of the cultivated land. Road accessibility refers to the distance from the cultivated land to the nearest road [52]. Centralized connectivity refers to whether the cultivated land is connected and to which degree of connectivity. In this study, the CONTIG landscape index was used to represent the centralized connectivity of cultivated land. The CONTIG index is a contiguity index, which can effectively assess the spatial connectedness of objects [53]. If road accessibility is smaller and centralized connectivity is larger, then the construction level of the cultivated land is better. The productivity capacity of cultivated land was evaluated from the perspectives of the high productivity capacity and the stable productivity capacity. Previous studies have shown that net primary productivity (NPP) derived from MODIS 17 A3 (MOD17A3) can effectively characterize the productivity level of cultivated land [54; 55]. The advantage of using NPP is that time-series data are readily available, and they can serve as a common comparable unit across different crop types [55]. In this study, we used the mean of NPP and the CV of NPP for three consecutive years to represent the high productivity capacity and stable productivity capacity of cultivated land, respectively.