Get ggmap basemap from (padded) sf object.
ps_sf_ggmap(x, pad, source, maptype)
A sf object.
A numeric vector indicating amount in metres to pad bbox. If vector of length 1, that amount is added to all sides; if vector of length 4 amount is added to left, top, right and bottom, respectively.
Google Maps ("google"), OpenStreetMap ("osm"), Stamen Maps ("stamen"), or CloudMade maps ("cloudmade").
Character string providing map theme. Options available are "terrain", "terrain-background", "satellite", "roadmap", and "hybrid" (google maps), "terrain", "watercolor", and "toner" (stamen maps), or a positive integer for cloudmade maps (see ?get_cloudmademap).
ggmap object.