# Maritime Traffic Evaluation Using Spatial-Temporal Density Analysis Based on Big AIS Data
## 5 Conclusions  
This study proposed a new method for density analysis of AIS data of the coastal waters in Korea. The data of cargo ships, tankers, passenger ships, and towing ships with customary traffic patterns were restricted to ship lengths of 60 m or more and ship speeds of 3 kts or more. To reflect the influence of the seasons, the data were collected over four-months, each month representing one of the four seasons. The analysis method calculated the occupancy time of each ship in each cell from the position and time information contained in the AIS data. The density distribution was determined by a descriptive statistical analysis and was normalized through a log-transformation of all density values. Finally, the calculated density was visualized using the stretch symbolization method to create a density map. The converted density values visualized using the stretch symbolization method can confirm the identification of major and distinct maritime traffic patterns. This approach differs from the density analysis methods widely used in existing maritime traffic research, and is valuable for confirming the maritime traffic pattern and density in the coastal area of Korea. The proposed spatial-temporal density analysis and visualization method constitutes a key technology for building a national maritime transportation network. This method can extract traffic routes through a quantitative analysis of big data and further identifies traffic networks. In addition, the density analysis results can be actively utilized for route planning by onboard navigation officers and captains. Judging from the accumulated records where numerous ships have safely completed their voyages, many ships have sailed along particular trends, having considerable reliability to the analysis result. A limitation of this study is that the density analysis ignores the influence of ship size on ship density. Suppose that a small ship and a large ship sail at the same speed and route through the same cell. The two ships occupy different areas and pose different degrees of risk to nearby passing ships. If the ship size is ignored, the calculated maritime traffic density may differ meaningfully from the actual traffic environment. Furthermore, the constructed traffic route might not secure the safety of large ships because it does not  
Figure 8: Comparison of ship traffic densities in the coastal area of Korea analyzed and visualized using two sets of methods: (**a**) [PERSON] et al. [31] used the top 50% of total traffic volume for route extraction via the line density analysis and quantile methods; (**b**) the present study uses the top 25% of the total traffic volume for main route extraction using spatial-temporal density analysis and standard-deviation-based stretch symbolization. reflect the traffic pattern of large ships with relatively small ratios. In future study, a ship-scale conversion factor based on ship tonnage, length, and width will be constructed by analyzing the specifications of ships passing through the coast of Korea. This factor will be used as a density weight in a more quantitative and advanced density analysis. Conceptualization, Y.-J.K., J.-S.L. and I.-S.C.; methodology, Y.-J.K., A.P. and L.F.; software, Y.-J.K., A.P. and L.F.; validation, Y.-J.K., J.-S.L., K.-K.Y., M.-S.L. and I.-S.C.; formal analysis, Y.-J.K.; investigation, Y.-J.K.; resources, Y.-J.K., A.P. and L.F.; data curation, Y.-J.K.; writing--original draft preparation, Y.-J.K.; writing--review and editing, I.-S.C.; visualization, Y.-J.K.; supervision, I.-S.C.; project administration, M.-S.L. and I.-S.C.; funding acquisition, M.-S.L. All authors have read and agreed to the published version of the manuscript. This research was supported by Korea Institute of Marine Science & Technology Promotion (KIMST), funded by the Ministry of Oceans and Fisheries (1525013332). Not applicable. This research was conducted with data provided by the Ministry of Oceans and Fisheries (MOF, Korea) for Ship Traffic Route research in 2021.