This is the visual definition icon responsible for specifying how a map background is displayed. It controls features such as coastlines, land and sea shading and grid lines.
The macro language equivalent is mcoast().
The Coastlines Editor
All of the parameters in this editor come directly from Magics, and are documented on the coastlines reference page.
Adding a user-supplied shapefile as a layer
If you have a shapefile with geographical polygons, this can be added to a plot via the Coastlines icon. The relevant parameters are Map User Layer, Map User Layer Name, Map User Layer Style, Map User Layer Colour and Map User Layer Thickness. To use an own shapefile, set Map User Layer to On, then set Map User Layer Name to the path to the shapefile, with the base file name of the file as the last element. For example if the path to the shapefile is /home/me/files and there is a shapefile called MyShape.shp in that directory, then we would set this parameter to /home/me/files/MyShape.
The following screenshot shows the result of loading a shapefile of UK roads into Metview:
