include a new geometry in nuts2json for the land mass.
show this new geometry as a background, above the sea rectangle and below the nuts/cntr geometries.
add option to show/hide country geometries
add option for the fill style of this land mass geometry.
Note that this land mass geometry is required for the value-by-alpha map. Otherwise, when changing the regions opacity, the blue of the sea will appear...
Note that this land mass geometry is required for the value-by-alpha map. Otherwise, when changing the regions opacity, the blue of the sea will appear...
The land mass polygon could be used to make coastal margin: https://observablehq.com/@jgaffuri/coastal-margin-with-css-stroke-width