I'd like to make a world map with a blue coloured ocean and transparent land surface (to be used later as an overlay). With:
map = GeoGraphics[
CountryData["World", {"SchematicPolygon", "Equirectangular"}],
GeoRange -> {{-90, 90}, {-180, 180}}, GeoBackground -> Transparent]
I get the opposite, i.e. ocean is transparent and land is coloured. How can this be reversed?