# Maritime Traffic Evaluation Using Spatial-Temporal Density Analysis Based on Big AIS Data
## 3 Results
### Creating Density Maps
#### 3.4.2 Density Maps by Ship Type  
Figure 6 shows the visualization results of the density calculations for each ship type. The traffic density of cargo ships was high along the coast from Incheon to Donghae, and the routes of ships entering and departing from major domestic ports were clearly evident. In addition to coastal routes such as harbor approach routes and coastal access routes, open-sea routes with low density values were clarified. However, tankers were reported at high density in Ulsan, which handles voluminous liquid cargo. Other tanker routes, namely, to Incheon, Pyeongtaek, Daesan, Gunsan, and Yeosu, demonstrated high densities too. The tanker density on the route around the coast was similar to that of cargo ships along the west and south coasts but lower than that of cargo ships along the east coast. Passenger ships were divided into domestic and international routes. The domestic passenger ships  
Figure 5: Histograms of logarithmically transformed density values representing raster pixel values. The red histogram shows the linear redistribution of the values originally lying between -1 standard deviation and +1 standard deviation from the mean over the entire observed range.  
traveled from Jeju to Mokpo, Wando, and Geomundo, along simple routes between Pohang and Ulleungdo, and along major routes between islands. The international passenger ships traveled between Japan and Busan and between China and Incheon, Pyeongtaek, and Gunsan. Towing ships demonstrated a more irregular traffic pattern than the other three ship types, with complex and variable routes. They included a route from the coast to the open sea (probably taken by rather large towns ships) and a route within the waterway (probably taken by small tug boats supporting port entry and exit).  
Figure 7a shows the result of merging the density analysis results across all ship types. By adding the four-month density analysis values of the cargo ships, tankers, passenger ships, and towing ships, we can determine the customary maritime traffic flows of major ships through the coastal waters of Korea. Open-sea routes were identified as routes in the ocean and the near-seas connecting coastal routes, whereas inland routes were identified  
Figure 6: Visualization of log-transformed density values by ship type using standard-deviation-based stretch symbolization: (**a**) cargo ships, (**b**) tankers, (**c**) passenger ships, and (**d**) towing ships.  
between islands and through relatively narrow waterways. Routes designated for entering and exiting ports, which can be potentially utilized under the current Maritime Safety Act, were identified, in addition to coastal access routes connecting coastal and inland sea routes with port entry and exit routes.  
The high-density routes were those that remained after sequentially reducing the total percentage of the stretch color ramp from 100% to the top 75%, 50%, and 25%. The route with the highest density, which circulates along the coast, was apparent even when only the top 25% of the stretch ramp was shown. After reducing the percentage of the stretch color ramp to 25% (Figure 7d), most of the open-sea routes disappeared and only the inland routes, coastal access routes, and coastal routes remained. These analysis results provide a quantitative scientific method for extracting and designating a major maritime traffic route  
Figure 7: Visualization of log-transformed density values for all ships using the standard-deviation-based stretch symbolization. The continuous color scheme of stretching is applied to (**a**) 100%, (**b**) the top 75%, (**c**) the top 50%, and (**d**) the top 25% of the full range.  
within the coastal waters of Korea because they allow an objective, accurate visualization of the main route.