# A New Parameter-Free Slope Unit Division Method That Integrates Terrain Factors
###### Abstract  
With increasing research on geological hazards and the development of geographic information technology, slope units play an increasingly important role in landslide susceptibility assessment and prevention work. The scientific and reasonable division of slope units directly impacts the accuracy and practicality of analysis results. Despite the significant progress in slope unit division techniques, most existing methods still have certain limitations, such as a strong dependence on manually set thresholds during the division process, resulting in low levels of automation and efficiency. To address this issue, a new parameter-free slope unit extraction algorithm that integrates terrain factors, called Terrain Factor Parameter-Free Slope Unit Division (TFFF-SU), is introduced. This eliminates the issue of manually setting parameter thresholds during the slope unit division process. This algorithm fully utilizes the terrain information provided by digital elevation models (DEMs) to accurately calculate the curvature, slope, and aspect data for each point. On the basis of the inherent consistency principles among slope, aspect, and curvature, object-oriented image segmentation technology is used to achieve slope unit division. We select Dongchuan District in Yunnan Province, China, as a test area to verify the TFFF-SU algorithm and conduct a detailed comparative analysis and validation of the results with those obtained via traditional hydrological analysis methods from both qualitative and quantitative perspectives. In the quantitative analysis, we utilize the size and shape of the slope units. The results indicate the following: 1 the slope units obtained with the TFFF-SU method are more uniform in size, avoiding issues with oversized or irregularly shaped units; 2 the slope unit shapes obtained with the TFFF-SU method are more reasonable, with about 70% of the units falling within a reasonable shape index range, compared to only about 32% with the hydrological method; and 3 the slope units produced by the TFFF-SU method align more closely with terrain authenticity, exhibiting a higher degree of topographical conformity. digital elevation model; slope unit; hydrological method; region growing; landslide 23 September 202424 November 20242 November 2024 29 November 2024 3 December 20242024 November 20242024 favor in landslide hazard prediction and assessment because of their unique characteristics [17]. The delineation of slope units directly corresponds to actual topographic structures, and, thus, slope units intuitively reflect surface slope changes and their close association with landslide formation mechanisms. Therefore, in recent years, many scholars have used slope units for landslide hazard risk assessment, aiming to obtain more realistic and targeted risk distribution maps and susceptibility zonation results. This information can be used to effectively guide disaster prevention and mitigation efforts, thereby minimizing the negative impacts of landslides on society, the economy and the environment [18; 19]. Early slope unit subdivision relied on manual operations, making the process cumbersome, error-prone, and highly subjective; thus, it is suitable only for small-scale applications. Currently, a widely used method for extracting slope units in geological hazard assessment research is the hydrological analysis-based [20; 21] framework first proposed by [PERSON] et al. [14]. The core of this method is to treat slope units as unique topographic units defined by the interweaving of ridgelines and valley lines [22] based on a digital elevation model (DEM). In this process, DEM preprocessing, including depression filling, terrain reversal, and other operations, is typically performed first to accurately identify watersheds and drainage paths.