I am looking for solution how one can add an underlying raster map background from a free source (= not from google, see ggmap).
This (ideal) solution should work seamlessly with the geom_sf() as I would like to show things on a map.
Another aspect would be that this underlying raster map solution should recognize (= be compatible with) the crs (coordinate reference system) embedded in the sf objects to be plotted on top of the map.
Thank you for your recommendations.
Yes, I assure you that I have already done in advance a quite wide search before asking.
Please note, that in my question I asked explicitly for free alternatives which rules out ggmap or any other solutions based on google API.
The third is an old article (5+ years), although the OpenStreetMap it looks promising this package was updated last time about 3 years ago, so it is questionable because the old java dependencies.
No, I don’t have the any raster map in advance, this is what I want to be fetched automatically and to be included as an underlying map layer in the plot.
A was too quickly dropping the ggmap when I have seen that the README.md starts with drawing the attention to changes in google API, and because this part of the documents is quite long (filling a complete screen in the browser) I never read the rest of this description.