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In order to load a coastline, click the (
) button. Make sure the coastline is in the WGS84 EPSG4326 WGS84 EPSG:4326 format.
When drawing on the map by clicking on the (
) button, use the LeftMouseButton (LMB) to click coastline coordinates and double click the LMB when you’re done. Now, the coastline can be deleted by clicking (
) or flipped (in order to make sure the offshore direction, which is indicated by the blue arrow, is correctly pointing in the offshore direction) by clicking (
).