# Maritime Traffic Evaluation Using Spatial-Temporal Density Analysis Based on Big AIS Data
## 2 Materials and Methods
### Analysis Area and Grid Division  
The coastal waters of the Republic of Korea, located in East Asia, were selected for analysis. Note that \(>\)90% of Korea's import and export cargo is transported by ships and the geographical characteristics of Korea have prompted the development of Korea's shipping industry [42]. Therefore, many ships pass via the coastal waters of the Republic of Korea and handle large volumes of cargo, primarily in the ports of Busan and Incheon. The complete area (including the territorial waters) and the exclusive economic zone (EEZ) as a partial area were selected for analysis. Figure 2 shows the approximate geographical location of the analysis area. The internal boundary is the territorial sea (the sea area adjacent to the territory), which comprises the coastal sea, the inland sea, bays, and straits. It extends to a width of 12 nautical miles from the baseline. The territorial sea includes multiple islands and dangerous zones such as low-depth areas requiring special attention for ship passage. The external boundary is the EEZ, a sea area up to 200 nautical miles from the baseline, where marine scientific research or installation and use of facilities is permitted.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Ship’s Dynamic Conditions** & **Reporting Interval** \\ \hline Ship at anchor or moored and not moving faster than 3 knots & 3 min \\ Ship at anchor or moored and moving faster than 3 knots & 10 s \\ Ship moving at 0–14 knots & 10 s \\ Ship moving at 0–14 knots and changing course & 3\({}^{1}\)/3 s \\ Ship moving at 14–23 knots & 6 s \\ Ship moving at 14–23 knots and changing course & 2 s \\ Ship moving at 23 knots or more & 2 s \\ Ship moving at 23 knots or more and changing course & 2 s \\ \hline \hline \end{tabular}
\end{table}
Table 1: Reporting intervals of Class A shipborne mobile equipment.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Categorization** & **[PERSON] et al.’s Study**[37] & **This Study** \\ \hline \multirow{6}{*}{Data period} & one week by season & one month by season \\  & 1–7 March 2018 & 1–31 March 2018 \\ \cline{1-1}  & 1–7 June 2018 & 1–30 June 2018 \\ \cline{1-1}  & 1–7 September 2018 & 1–30 September 2018 \\ \cline{1-1}  & 1–7 December 2018 & 1–31 December 2018 \\ \hline Ship types & cargo ships, tankers, passenger ships, towing ships \\ \hline Ship length & over 60 m (\(\geq\)60 m) \\ \hline Ship speed & - & over 3 knots (\(\geq\)3 kts) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of the AIS data used in the analysis of [PERSON] et al. [37] and the present study.  
A density analysis requires a grid of certain-sized cells within the analysis area [34]. Both Marine Cadastre and the Northeast Ocean Data portal, an integrated maritime information system in the United States, supply information related to maritime traffic (particularly vessel transit counts) in 100-m cells [43]. European marine observation and data network (EMODnet), supported by the EU's integrated maritime policy, adopts 1-km cells to cover all EU waters and certain adjacent areas [44]. In this study, the cell size was selected as 1 km considering the speed and capacity problems caused by processing and calculating big data. To prevent unnecessary computation and excessive data size in the cells of the analysis area, the portions overlapping land were removed. The final set of cells was only composed of sea area. The resulting grid contained 323,691 cells, including the harbour along the coastlines.