# A New Parameter-Free Slope Unit Division Method That Integrates Terrain Factors
###### Abstract
Although this method is theoretically universal and practical, in actual applications, especially under complex topographic conditions, it may produce some small cross-sectional units that do not conform to actual geomorphological features, as well as overly elongated units in the flow direction [15; 23; 24; 25]. These require extensive manual intervention and correction to improve accuracy and practicality. To avoid these issues, many scholars have made improvements to this method. For example, [PERSON] [26] divided units by classifying landform elements through image analysis, combining layers of elevation, profile curvature, plan curvature, and slope data. [PERSON] et al. [15] proposed the curvature watershed method [27], in which the boundaries of convex and concave geomorphological elements are extracted using positive and negative curvatures to obtain slope units. However, this method is essentially a hydrological analysis method. [PERSON] et al. [16] developed a professional software tool called rslopeunits [28; 29], integrated into the GRASS 6.4 GIS software, for delineating slope units. It uses advanced algorithms to automatically identify and extract drainage lines and ridgelines in the terrain and construct precise slope units based on these key topographic features. The method incorporates an adaptive algorithm that allows for the flexible and accurate delineation of slope units through an iterative process [30]. However, the effective application of this software relies on the user's reasonable setting of internal parameters, which requires certain levels of geological and geomorphological knowledge and a geographic information system (GIS) technical background. [PERSON] et al. [24] used morphological image analysis methods combined with logical algorithms to process DEM data, enabling the precise extraction of ridgelines and valley lines as a basis for slope unit delineation. Although this image analysis technique performs well in specific scenarios, especially in evaluating the stability of slopes formed by infinite boundaries or artificial excavations, its applicability is limited in cases with highly complex and variable mountainous terrains. Additionally, [PERSON] et al. [25] proposed a multiscale segmentation-based slope unit delineation strategy. This method can be adapted to assess geomorphological changes at multiple scales by subdividing terrain data at different scales, promoting detailed and comprehensive slope unit delineation. However, the implementation of this method involves cumbersome input parameter calculations and requires high computational power and in-depth theoretical support, thus posing a challenge in practical cases. In summary, diverse and distinct methods have been developed for the extraction and analysis of slope units. However, in the existing slope unit division techniques, some common problems and challenges are inevitably faced. A common challenge is that many methods require manual threshold setting during execution [10; 31], where the choice of parameters is crucial in slope unit division. Even the slightest error in these parameters can lead to overly dense or sparse slope units, necessitating frequent and lengthy trials to determine suitable parameters. This greatly increases the subjectivity of the division process, potentially leading to unstable extraction results due to differences in individual experience. To address this issue, we use information obtained from a DEM (i.e., homogeneity constraints in terms of terrain). By avoiding manual parameter settings, the slope unit subdivision is automated. This new method eliminates the complex parameter setting process, significantly reducing subjectivity and uncertainty in operation while improving the stability and consistency of the subdivision results. A novel and efficient slope unit extraction method that does not require manual parameter setting is proposed. We selected the complex terrain of Dongchuan, Yunnan, as the study area and used DEM data to perform slope unit division.