## 2 Materials and Methods
### Preprocessing and Statistical Analysis of AIS Data Used for Analysis  
The term AIS data refers to a device that allows for the transmission and reception of various information based on the vessel's movement. This information is navigational  
\begin{table}
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**No. ** & **Latitude** & **Longitude** & **No. ** & **Latitude** & **Longitude** \\ \hline Area 1 & 36.50\({}^{\circ}\) N–37.60\({}^{\circ}\) N & 124.50\({}^{\circ}\) E–127.00\({}^{\circ}\) E & Area 9 & 33.10\({}^{\circ}\) N–34.00\({}^{\circ}\) N & 127.20\({}^  
equipment that aids in the prevention of ship collisions as well as equipment that aids in receiving ship information on land and advising on arrival and departure. The AIS data generated here are stored in real time in a vast amount and help decision making by deriving meaningful results [33]. This database stores AIS data for about two years, from 1 January 2018 to 31 December 2018 and from 1 September 2019 to 31 August 2020. The data capacity is saved in the form of a 1.1 TB comma-separated variable file. Static and dynamic data are the two types of data. Static data represent the ship's unique information and includes MMSI, name, type, IMO number, callsign, length, draft, and gross tons (GTs). In addition, dynamic data means data that changes when a ship operates, and it includes MMSI, date, latitude, longitude, SOG, COG, and heading. The MMSI value is used to combine these two types of data. For preprocessing, Python was used. The total capacity of all AIS data passing through Korea per day is approximately 1.5 GB, with approximately 20 million data points. To increase the efficiency of the data capacity and analysis speed, the area was divided into 16, and to secure the main routes of commercial ships, it was extracted into four categories: cargo ship, tanker ship, passenger ship, and towing ship. Furthermore, in the case of small ships and fishing vessels, the ship's operation pattern is free and irregular, so the ship's size was classified as 60 m or greater [4]. As the distance from the land increases, the data loss rate occurs owing to the limitations of AIS. Table 2 displays the database capacity as well as the results of dividing the vessel type and vessel length for use in the analysis. The characteristics of ship operation vary according to the season. Typhoons primarily occur and pass through the seas of Northeast Asia during the summer and autumn seasons, and some factors, such as tropical cyclones, have an impact on ship operations. As a result, one week of data is extracted for each of the four seasons of 2018: spring, summer, autumn, and winter. Here, the days when typhoons and tropical cyclones do not occur are selected. As a result, traffic volumes were extracted from 1 to 7 March, from 1 to 7 June, from 1 to 7 September, and from 1 to 7 December. The Republic of Korea's sea area was divided into 16 areas based on the data extracted in this manner to efficiently use it for analysis. Table 3 displays the statistical characteristics of the data used in this study. \begin{table}
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The total number of data from analysis Areas 1 to 16 is about 62 million. Although some analysis areas have overlapping regions, it is used to ensure the smooth connection of maritime traffic routes. In Korea, Analysis Area 7 has the most data. The sea area with representative ports including Busan and Ulsan has the largest amount of data. In addition, this sea area contains Korea's representative container port, oil tanker port, and car carrier port. COG is primarily used to examine ship navigation patterns. Although there is a limit to suggesting the movement of all ships as an element that informs the ship's direction, the pattern can be outlined in a large frame. AIS data have a different transmission/reception interval depending on the ship's SOG and status [34]. The SOG of a ship expresses the relative speed of the ship relative to the Earth's surface.