# GIS Approach for Expressing Structural Landforms: Forms, Elements, and Relationships
## 3 Experiment and Discussion  
In this study, \"Qixia Mountain\" and \"Gaoli Mountain\" in the Ningzhen Mountain Range were selected as test cases, and the spatial morphology of the test objects was abstracted into spatial objects and their mutual relationships. Based on XML, the SLML of \"form-element-relationship\" was designed. The language was used to map the SLML and object relational database, graphically express the SLML spatial and range set association, and construct the topological relationship of SLML spatial objects. The key to the experiment was to abstract the structural landform elements and their relationships into spatial objects and topological relationships. Based on the types and characteristics of structural and geomorphic elements, the geometric types, attribute fields, and subtypes of spatial objects were established. The relationships between structural landform elements were abstracted into topological relationships. Based on the type of structural landform, topological names and rules of spatial objects were developed. (1) GIS expression of structural landforms on Qixia Mountain  
Figure 4: Construction of spatial objects and topological relationships. (**a**) Mesa; (**b**) Anticlinal Mountain; (**c**) Synclinal Mountain; (**d**) Anticlinal Valley; (**e**) Synclinal Valley; (**f**) Cuesta; (**g**) Hogback Mountain; (**h**) Fault Block Mountain; (**i**) Fault Valley. Qixia Mountain is a block mountain with straight boundary lines and steep slopes. It is composed of three mountains from south to north and has the highest conical peak. Qixia Mountain is characterized by massive faults. The occurrence of rock strata is relatively steep, and the axial plane is nearly upright or slightly reversed to the southeast. Thrust faults are relatively developed, and there are more than ten of them with large scales, all of which strike in the NNE direction, and most of them dip in the NNW direction. The dip angles are all larger than 70\({}^{\circ}\), forming a wide fault fracture zone composed of tectonic lenses and fault gouges, exhibiting the characteristics of hanging wall thrusting. In terms of structural geomorphology, Qixia Mountain is a fault block mountain, and its elements can be abstracted into three types: \"fault wall\", \"fault line\", and \"ridge line\". Accordingly, the geometric types, attribute fields, and subtypes are designed for these three spatial objects of structural landforms, namely, \"Fault_Wall_FBM\", \"Fault_Line_FBM\", and \"Ridge_Line_FBM\". The morphology of a structural landform is described by the relationships between the various components (the elements of the structural landform). The morphological characteristics of the fault block mountain are as follows: the fault line overlaps with the ridgeline, and the upper and lower layers of the fault wall show relative displacement. Its spatial relationship can be expressed as the \"fault wall (upper wall) boundary must be covered by the boundary of the fault wall (bottom wall)\" and the \"fault line must be covered by the feature class of the ridgeline\", as shown in Figure 5. Its graphical representation is shown in Figure 6.  
The SLML expression of the forms-elements-relationships for Qixia Mountain is as follows, where the geometric elements are based on the geometric form types of Esri.