Draw all map layers
plot.MapLayers.RdS3 plot method that draws (in order) the filled base (ocean or land),
coastlines, optional grids, optional borders, and optional center line.
All drawing is done with add = TRUE; initialize your plotting device
beforehand (e.g., plot(0,0,type="n", ...)).
Usage
# S3 method for class 'MapLayers'
plot(x, ...)