## 1 Introduction  
The Regional Geochemistry-National Reconnaissance (RGNR) project [1] covers over 7 million km\({}^{2}\) of China's land surface since its implementation in 1979, primarily focused on mountainous and hilly areas [2]. In the RGNR project, each sampling grid is 4 km\({}^{2}\) corresponding to a scale of 1:200,000. In each grid, four sub-samples were collected in 1 km\({}^{2}\) and then were combined to form a composite sample [3], and 39 geochemical items including major components (i.e., SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\), K\({}_{2}\)O, Na\({}_{2}\)O, CaO, MgO, Ti,P, and Mn) as well as Ni, Sn, Li, etc., were analyzed [4; 5]. The Multi-Purpose Regional Geochemistry Survey (NMPRGS) project [6] has been implemented since 1999 in China, primarily focused on the basin and plain areas, and 54 geochemical items, including major components and Ni, Sn, Li, etc., were analyzed. The database compiled by these two projects [7] and the geochemical maps and geochemical anomaly maps produced based on the data have played significant roles in the exploration of mineral resources in China [8; 9; 10]. The Mojiang area in Yunnan Province, an important Ni ore gathering area in China, has completed relevant survey and data collection work. This paper draws geochemical maps and geochemical anomaly maps on Ni-based on these data, providing a reference for Ni deposit exploration in the areas. Regarding geochemical maps which focus on the analytical values of elemental concentrations, there are three traditional methods commonly used: the cumulative frequency method, the logarithmic interval method, and the mean-standard deviation method [11]. As the scope of research areas and the accumulation of data continue to increase, the limitation of traditional methods that rely on the amount of data has gradually become apparent [12; 13], which further results in the inability to compare across different areas and elements. In recent years, to overcome the limitations of traditional methods, [PERSON] et al. [13] proposed a new approach to Cr geochemical map as the fixed-value method. Later, [PERSON] et al. [11], [PERSON] et al. [12], and [PERSON] et al. [14] further developed the fixed-value method for Sn, Li, and Mo on 19 levels, respectively. This 19-level fixed-value method is an objective method to classify elemental concentrations and facilitates the comparison across different elements and areas. However, the specific levels for Ni classification have not yet been proposed. On geochemical anomaly maps which focus on the relatively high values (or the anomaly values) of elemental concentrations or other geochemical indices [15], the methods commonly used in determining anomalies can be divided into two types: the fixed-value method and the unfixed-value method [16]. Geochemical anomaly maps created using the fixed-value methods (e.g., the mean-standard deviation method, cumulative frequency method, fractal method, etc. ), can be viewed as parts of the geochemical map (i.e., the background areas with low concentrations are covered) [12]. An apparent limitation of the fixed-value methods is that they ignore the influence of different lithologies on elemental concentrations [13]. Regarding the unfixed-value method, a method called seven levels classification [16; 17] was proposed, which is an objective approach for determining anomalies not influenced by the lithologies and the weathering degrees of samples [4; 5] and facilitates the comparisons across different elements and areas [11]. Based on the regional geochemical exploration data of the Mojiang area, which is rich in Ni resources in Yunnan province, China, this paper first proposes the 19-level fixed-value method for Ni. Then, this new method is used to draw geochemical maps and compare them with different elements. Subsequently, a seven-level classification method is used to create geochemical anomaly maps, also with a comparison among different elements.