Use constraints: Data can be used freely given that the source (HELCOM) is cited.

The grid is based on the EEA reference grid, that is developed based on the recommendation at the 1st European Workshop on Reference Grids in 2003 and later INSPIRE geographical grid systems.

The grid is first downloaded from the EEA website, and cut to cover the grid cells, where at least some part of the cell is within the Baltic Sea area, using the "HELCOM marine area" data set, that is the basis for all HELCOM Assessment unit data sets.

The second version of the grid "HELCOM 20x20km Baltic Sea grid without land areas" is further edited to include only the marine areas within the grid cells. This means that all land areas are removed within the grid cells, including the mainland coastline and all islands. This is done using the same "HELCOM marine area" data set, as above.

The coding system is developed by EEA, and is composed of cell size and cell coordinates. The cell size is denoted in meter (m) for cell sizes below 1000 m and kilometre (km) for cell sizes from 1000 m and above. Examples: a 100 meter cell has an identifier starting with “100m”, the identifier of a 10000 meter cell starts with “10km”.

The coordinate part of the cell code reflects the distance of the lower left grid cell corner from the false origin of the CRS. In order to reduce the length of the string, Easting (E) and Northing (N) values are divided by 10 n (n is the number of zeros in the cell size value). Example for a cell size of 10000 meters: The number of zeros in the cell size value is 4. The resulting divider for Easting and Northing values is 10 4 = 10000.

Further details

About the EEA reference grid: https://sdi.eea.europa.eu/catalogue/srv/api/records/aac8379a-5c4e-445c-b2ef-23a6a2701ef0/attachments/eea_reference_grid_v1.pdf

INSPIRE Data Specification on Geographical Grid Systems: https://knowledge-base.inspire.ec.europa.eu/publications/inspire-data-specification-geographical-grid-systems-technical-guidelines_en