use ichoropleth function in rMaps to plot other countries
You can use a custom layer for your map, but first you will need to convert your data to TopoJSON. I followed these instructions http://bost.ocks.org/mike/map/ to convert my shapefile to TopoJSON. In your ichoropleth function you can specify your map as follows:
d1$set(geographyConfig = list(dataUrl = "https://dl.dropboxusercontent.com/file_name.json")For more info on this topic check this post:https://github.com/ramnathv/rMaps/issues/6. or take a look to this repo for a working example https://github.com/Arevaju/shiny-maps.
Cheers!