The key idea is that `coord_sf()` now has a default coordinate system that it uses for any objects that are not sf (i.e., don't come with their own coordinate information). The default is longitude/latitude, which makes it super easy to, for example, mark a specific location. 2/n 
This works with essentially any geom, e.g., we can mark a couple of cities and draw an enclosing polygon. 3/n
As a consequence, we can now use `annotation_map()` in combination with `geom_sf()` and `coord_sf()`. `annotation_map()` draws regular polygons in long/lat space. 4/n
Limits are assumed to be in the default coordinate system, so we can now provide them as long/lat. 5/n
There's an important safety net when you don't want any of this: Set `default_crs = NULL` and you revert to the old behavior. For example, then you have to set limits in transformed coordinates. 6/n
If you find yourself having to work in projected coordinates, you may find the function`sf_transform_xy()` useful. It can transform regular data frames of coordinates from one coordinate system to another. 7/n
(This function is used internally by ggplot2 to calculate the coordinate transformations. It turns the data frame into sf points and then transforms them using the sf::st_transform() function.) 8/n
That's it for now. If you run into any issues, please ping me or file an issue on github. I'll close with one last example, using ggrepel and an unusual projection from the top of the pole. 9/9
