# Mapping Abandoned Cultivated Land in China: Implications for Grain Yield Improvement
## 2 Materials and Methods
### Methodology  
#### 2.2.1 Identification of Abandoned Cultivated Land  
Considering the existing studies on abandoned cultivated land, there is a lack of an accurate definition of abandoned cultivated land worldwide [41; 42; 43; 44]. According to the Land Administration Law of the People's Republic of China and actual cultivated land use in agricultural production, we defined abandoned cultivated land as cultivated land that has remained dormant for a period of over two consecutive years, devoid of any agricultural production activities, and continues to be unproductive or barren. Namely, from the perspective of land cover, it is transformed from planting crops to the bare surface, rolling surface, grassland, etc. Thus, based on the types of the contents and indicators of the Census of National Geographical Conditions (GDPJ01-2013) to distinguish between the criteria and the specific realities of the study area, this study preliminarily determines the land use types with the characteristics of barren land cover within the scope of cultivated land in 2017, including natural grassland, rolling surface, manual stacked substance, desert, and bare surface, as the main types of abandoned cultivated land. Simultaneously, based on the notion of abandoned cultivated land and its objective evolutionary patterns, this research has developed the following guidelines for identifying abandoned cultivated land: Based on the land use type in 2015, there were cultivated land plots a, b, c, and d in 2015; in 2016, plots a and b were still under cultivation, while plots c and d had evolved into grassland, rolling surface, manual stacked substance, or desert and bare surface; in 2017, plot a was still under cultivation, plot b was transformed into grassland, rolling surface, manual stacked substance, or desert and bare surface, plot c was transformed into cultivated land and realized continued cultivation, and plot d was still under the cover state of grassland, rolling surface, manual stacked substance, or desert and bare surface. It can be seen that plot c returned to the state of cultivation one year after the cessation of cultivation, which fails to meet the defined criteria for abandoned cultivated land in this study. Therefore, this study believes that plot c does not constitute the abandonment of cultivated land. However, no agricultural production activities have been carried out in plot d for two consecutive years, and the land cover has always been barren or bare. Therefore, plot d is considered the cultivated land abandonment in 2017 (see Figure 1). According to the above identification guidelines, the procedure for extracting abandoned cultivated land in this study is as follows: The spatial extent of abandoned cultivated land was defined using the \"cultivated land\" category derived from the land change survey data in 2015. The intersection was performed between the land use change survey data layer of 2015 and the national geo-information survey data layer of 2017. Based on the classification criteria outlined in the Contents and Indicators of the Census of Geographical National Conditions (GDPJ01-2013), we preliminarily identify the land use types with the characteristics of barren or bare land cover within the scope of cultivated land in 2017, which includes natural grassland (with the land type code of 0411, 0412, and 0413), crush and trample the surface (with the land type code of 0718), manual stacked substance (with the land type code of 0821, 0822, and 0829), desert and bare surface (with the land type code of 0910, 0920, 0930, and 0940) to form vector files of abandoned cultivated land patches. In addition, to validate the accuracy of abandoned cultivated land extraction, this study uses Google Earth satellite images from 2017 to select 762 plots across 62 counties within the study area, and the correct rate reached 85.65%, indicating that using a combined method of land use change survey and national geo-information survey data to pinpoint and retrieve unused cultivated land is highly accurate.