## 4 Mobile Phone Data  
In 2015, there were about 57 million mobile phone users in Korea, which is equal to 1.13 mobile phones per person on average. SKT, one of three wireless telecommunications operators in Korea, has held about half of the country's total mobile phone accounts. Therefore, SKT expanded mobile phone data to include the total users in Korea, using the country's market share rate. In this study, we used SKT's complete mobile phone dataset, representing the total population of mobile phone users. The mobile phone data include information about the number of mobile users as well as locations of these users, including their home location and existing location of the phone user. The existing  
Figure 1: Honam high-speed railway (HSR) line and cities for a case study in Korea. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Conditions** & **Existing Line** & **New Line** \\ \hline Route Info. & Seoul-(Daejeon*)-lksan-jeongeup-Mokpo & Seoul-lksan-jeongeup-(Kwangju*)-Mokpo \\ \hline Distance (km) & 352 & 330 \\ Travel Time (min) & 202 & 149 (\(-\)26\%) \\ Operation speed (km/h) & (Seoul)-(Daejeon): 300, & Seoul-lksan-jeongeup - \\  & Iksan-Mokpo:150 & (Kwangju)-Mokpo: 300 \\ \hline \multicolumn{2}{c}{Fare (§, one-way)} & \multicolumn{1}{c}{§42 (Seoul-Mokpo)} & \multicolumn{1}{c}{§50 (Seoul-Mokpo)} \\ No. of passengers (million/year) & 669 & 950(+42\%) \\ \hline \hline \end{tabular} Note: (*) represents a city not analyzed in this study.  
\end{table} 
Table 1: Comparison Before and After the Introduction of the Honam HSR line. location of the phone user is pointed on a grid cell of 50 \(\times\)50 m, called a P-cell. Table 2 presents information on mobile phone data. The data are the daily mobile phone records, grouped by age and gender and consist of 16 columns, including dates; locations (X- and Y- coordinates) in a 50 \(\times\) 50 cell. In a P-cell, a user exists at any time of the day; the number of mobile phone users that are classified by six age groups by gender; and the home location of the user. It is a daily-based record and double counts are not allowed in the same cell and in the same day. If he/she exists in the same cell in the same day even at different times in a day, he/she is counted as one. It should be noted that the number of records is not equal to the mobile population. Each record is constructed based on a combination of two locations, including a 50-m grid cell and a home location; that is, one record represents the number of people, who are in the same 50-m grid cell in each hour, as well as the same home location. For instance, even if two mobile phone users exist at the same grid cell in the same hour of the day, their records appear in separate rows if their home locations are different. As the Honam HSR opened in April 2, 2015, we use the mobile phone records of one week--from March 16 (Monday) to March 22 (Sunday) in 2015 and from March 14 (Monday) to March 20 (Sunday) in 2016. In order to analyze the diverse geographical impact of the HSR, we classify the mobile phone data into two levels. One is the station level, wherein mobile phone data are observed at a station area used for analyzing the changes in the volume of mobile population and access distance from an individual user's home to the HSR station. The other level is the city level, wherein the change in hotspots after the opening of the HSR is investigated; their compactness at the station periphery is also investigated. For this analysis, we aggregated the mobile population at a P-cell to those at a station (as shown in Figure 2) and city boundary using ArcGIS. Then, we averaged the daily data by weekday and weekend. Table 3 shows that the final extracted numbers of mobile phone records differ from each station.