## 3 Construction of Spatial Database  
It is necessary to determine the factors affecting the land subsidence of a coal mine area. The lithology of the overburden rocks, geological discontinuities, ground slope, scope of the mined cavity, extent and depth of mining, mechanical characteristics of the rock mass rating (RMR), and flow of groundwater are considered the main factor [11; 25; 27; 28]. Spatial data for all of these factors may be difficult to collect and may not be available. The available spatial databases used in this study were constructed using ArcGIS 10.5. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Location** & **Structure** & **Elevation (m)** & **Mining Depth (m)** & \begin{tabular}{c} **Thickness (m)** \\ **and Slope of Coal** \\ **Seam** \\ \end{tabular}  & \begin{tabular}{c} **Subsidence** \\ **Depth (mm)** \\ \end{tabular}  & \begin{tabular}{c} **Other** \\ **Other** \\ \end{tabular}  \\ \hline S1 & Railway & 885 & 20–30 & \begin{tabular}{c} 1–2 \\ 40–50° \\ \end{tabular}  & \ \begin{tabular}{c} 90 \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ \end{tabular}  &
\begin{tabular}{c} -The coal seam is oblique to the railroad. \\ - Shallow depth of mine \\ -  
The surface geology with cross section lines was constructed using a digital geological map with 1:50,000 scale [29] published by the Korea Institute of Geoscience and Mineral Resources (KIGAM). The geological formations include the Manhan, Jangseong, Hamboaegan, Dosagog, and Alluvium horizons (Figure 2a, Figure 3). Most of the coal was mined from the Jangseong Formation with a thickness of 80-15 m [22; 30]. This formation includes four to five cyclothems consisting of dark-gray sandstone, black shale, and coal seam (Table 2). The land use was constructed from a digital land characteristics map with 1:5,000 scale [31] supplied by the National Geographic Information Institute (NGII). Land use for the study area was classified into 10 categories: wood land, railroad, river, field, plot, road, school, hybrid land, brook and unclassified area (Figure 2b). The rate of land subsidence compared to the area of each category was higher in the railroad and school classes [21]. The surface slope was calculated from a digital elevation model (DEM) constructed from a digital elevation contour line with 1:5000 scale [32] published by NGII (Figure 2c). Surface slope was considered an affecting factor because land subsidence can change surface slope, differential horizontal strain, and vertical displacement [33]. Distance from drift was calculated from a digital drift map provided by the Mine Reclamation Corporation (MIRECO) [26] (Figure 2d). The map is important because it identifies the areas of mining activity in this region. Geological discontinuities are considered to be factors affecting land subsidence, but no geological lineaments appear in the study area on the available 1:50,000 geological map. Therefore, geomorphological lineament was visually extracted from an IKONOS satellite image by a field geologist (Figure 2e). If the location is near a lineament, the value of distance from lineament is low. The borehole data in the study area, provided by the Mine Reclamation Organization (MIRECO) in 1996 [26], were collected from 29 boreholes (Figure 1 and Table 3). The depths of the boreholes ranged from a minimum of 19.5 m to a maximum of 200 m. The data included hydrologic properties and rock mass information [34]. The depth of groundwater, rock mass rating (RMR), and permeability were obtained from 16, 19, and 6 boreholes, respectively (Table 3 and Figure 2f,g,h). The maximum depth of groundwater was 42.5 m. On the railroad, the upper part of the railroad had a deeper groundwater depth and lower elevation than the lower part of the railway. The RMR was classified as classes 1-5, representing very good, good, fair, poor, and very poor, respectively. In this study, the RMR ranged from 2-4.5. The lowest RMRs appeared in the northwest and southeast portions of the railroad.