Use constraints: Data can be used freely given that the source is cited (following creative commons license CC-BY). The source should be cited as: “HELCOM HOLAS 3 Dataset (2023)".

The density map is based on a grid from the European Environment Agency (EEA) and is following the INSPIRE geographical grid systems. It is dividing the Baltic Sea into cells of 1 km by 1 km.

For each month, a value was assigned to each cell of the grid. The value is the number of trips crossing the particular cell. A trip is defined as a movement of a ship between two ports or from/to outside the Baltic Sea. A total of 245 ports and 5 areas defining the borders of the Baltic Sea were used to generate the trips as lines. The lines are joining the AIS signals (points) for each ship traveling between the ports or from/to outside the Baltic Sea. The lines were applied to the grid to count the total number of lines crossing each cell for each month. The final map displays the average per cell from 2016 to 2020.