The ocean layer (table osm_ocean_polygon insert by `make import-data`) is made from squares that have a 10m buffer.
This creates extra geometry in vector tiles as:
Union of full ocean squares should decrease the size of the water layer.
there are 8042 polygons (squares, 5 points, more then 100km<sup>2</sup>), which was reduced to 22 polygons - 1184kB vs 40kB respectively.
In mbtiles should be the size reduction even more significant, due to the creation of more polygons based on a 10m buffer of each square.
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