## 9 Conclusions  
The large amount of data collected from mobile communications provides the spatial-temporal locations of phone users, which acts as a source for investigating urban issues related to mobility behavior and the spatial-temporal demographic dispersion of a city. This study examined the potential use of mobile phone data for empirical analysis of the impact of HSR in terms of mobile population changes by gender and age group, travel distance, density of access distance, location of hotspot changes, and compactness of hotspots from the HSR station. In order to accomplish this, we choose \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**City**} & \multicolumn{2}{c}{**Before**} & \multicolumn{2}{c}{**After**} \\ \cline{2-5}  & **Number of Hotspots (pop. \textgreater{} 50)** & **Compactness** & **Number of Hotspots** & **Compactness** \\ \hline Iksan & 127 & 0.186 & 224 (\(\Delta\)76.4\%) & 0.101 (\(\Delta\)45.5\%) \\ \hline Jeongeup & 6 & 0.987 & 9 (\(\Delta\)50.0\%) & 0.831 (\(\Delta\)15.8\%) \\ \hline Mokpo & 119 & 0.762 & 229 (\(\Delta\)92.4\%) & 0.379 (\(\Delta\)50.2\%) \\ \hline \end{tabular}
\end{table} 
Table 6: Number of hotspots and compactness in the HSR station catchment area. a case study of the Honam HSR line, introduced on April 2, 2015, which directly connects the capital city, Seoul, to several cities, namely, Iksan, Jeongup, and Mokpo, located 200-300 km south of Seoul. We use the mobile phone records of one week of data, from March 16 (Monday) to March 22 (Sunday), 2015; and from March 14 (Monday) to March 20 (Sunday), 2016, for a before-and-after study. From the basic statistical analysis, we found that the mobile population is seen to increase in Seoul and all three cities during weekdays. All age groups show an increased mobile population; however, those over 60 years old showed a decrease. Older people usually make a relatively short trip in Korea, and use other intercity modes of travel, as they are sensitive to the increased fare of HSR and have a surplus of time. Among three cities, Mokpo, which is 300 km away from Seoul, only has a positive value of the Wilcoxon signed ranks test statistic W for males over 60, and the value of test statistic W for women over their 60 s is negative. However, the magnitude of the value is smaller than that of other cities. Therefore, we found that the longer the travel distance, the higher the number of people who would like to take the HSR, no matter what age group. By developing the map of mobile population changes with respect to travel distance, we can easily evaluate whether the mobile population increases due to the HSR. From the results, we found that the mobile population within 200 km of Seoul is not shown to increase, because the operation speed of the HSR line is almost the same as that of the existing line connecting Seoul to Daejeon, close to Iksan city, approximately 200 km away from Seoul. This illustrates that a resident within 200 km of Seoul did not change their travel pattern due to the HSR in Korea, because the travel time saved is not enough to warrant a change in transport mode. The HSR fare went up by approximately 30% and hindered the attraction of the mobile population. However, more people from Jeongup and Mokpo are observed in Seoul, which is seen to be a \"straw effect\". However, we cannot determine whether this effect will continue. Unlike Seoul, Iksan and Jeongup have an increased mobile population within 150 km, which decreased at over 200 km and 150 km-200 km, respectively. Iksan did not attract more people from the northern part of Seoul, Kyeonggi-do, while Jeongup attracted less people from Seoul after HSR. The reason for this cannot be explained, but the attraction may vary depending on the size of city and business structure. However, Mokpo shows increased mobile population at all distance levels, which indicates that the HSR line had a positive influence on the relatively short-distance travel between the neighboring cities, and long-distance travel as well.