# GIS Approach for Expressing Structural Landforms: Forms, Elements, and Relationships
## 2 GIS Approach for Expressing Structural Landforms
### Descriptions of Elements, Characteristics, and Relationships  
First, the type of structural landform is defined. Structural landforms are geomorphic features controlled by the underlying geological structure and the distribution of rocks with different values of resistance to erosion. To delineate the basic geomorphic and genetic types, the structural landforms in this paper are divided into four basic structures (horizontal strata, fold, monoclinic, and fault structures) and nine landform types (square mountains, anticlinal mountains, synclinal mountains, anticlinal valleys, synclinal valleys, single mountains, hogback mountains, fault block mountains, and fault valleys), as shown in Table 1.  
Second, each component of the structural landform is abstracted into various elements. Structural landform elements are the various components of structural landform morphology. Due to the particularity of their evolution, structural landforms cover many components of geology and geomorphology. Their components are abstracted into nine elements, i.e., the rock layer, stratum, rock, fault disk, fold core, fold axis, stratigraphic boundary, fault line, contour line, ridge line and valley line, as shown in Table 1.  
Third, the characteristics of structural landform elements are analyzed and quantified. Geomorphic elements include the occurrence, material composition, and age of formation. For example, strata are divided into horizontal, vertical, and inclined strata according to the geometric characteristics of occurrence; rocks are divided into soft, medium-hard, and hard rocks according to their hardness characteristics; and the stratigraphy is classified as Quaternary to Cambrian according to the stratigraphic chronology. Finally, we describe the structural landform morphology via the relationship between its components. For example, Fang Mountain can be described as \"a horizontal rock formation with a hard top whose contours coincide with the boundary of the rock formation\", as shown in Table 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{1}{c}{**Basic Landform Type**} & \multicolumn{2}{c}{**Genetic Type**} & \multicolumn{2}{c}{**Morphological Types**} & \multicolumn{1}{c}{**Element Type**} \\ \hline
**Land Relief** & **Altitude** & **Genesis** & **Secondary** & **Structural** & **Secondary Form** & **Structural** \\  & & **Genesis** & **Form** & **Secondary Form** & **Landform** \\ \hline  & & & Stratum & Horizontal & Mesa \\  & & & fluctuation & Stratum & Pop-up Relief \\  & & & structure & Pop-down Basin & \\  & & & & & \\ \cline{2-5} Plain & & & Stratum & Anticlinal & Terrane \\  & & & Mountain & Stratum & Stratum \\  & & & Spchinal & Rock \\  & & & bonding & Mountain & Fault Wall \\  & & & & Anticlinal Valley & Core of Fold \\  & & & & Synchronal Valley & Folding Axis \\  & & & & & Stratraphic- \\  & & & & & Boundary \\  & & & inclination & structure & Fault Line \\  & & & & & Contour Line \\  & & & & Fault & Ridge Line \\  & & & & Block-Mountain & Valley Line \\  & & & & Fault Valley & \\  & & & fracture & Fault structure & \\  & & & & Thrusts & \\  & & & & Horst & \\  & & & & Graben & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Classification of structural landforms (genesis, morphology, and element types).