Examples of generating maps

For mapping, it seems worthwhile to encourage combining the compendium data with the rnaturalearth package. We already have the code for mapping compendium countries from the first paper; it would be helpful if we made it easier for people. From Benjamín:
>I think I was looking for the file (if any) you used to map the countries in the HMC metadata to the world map data that comes with rnaturalearth. In the end, I was able to reproduce the HMC map by regrouping subregions in rnaturalearth metadata to match the 7 major regions you used.

Start by locating the existing code used to map compendium countries in the first paper and compare it with the country and region metadata from rnaturalearth. Document or expose an example that reproduces the map, including the regrouping needed to match the seven major regions; done means users can follow the example to generate the map.

Scritto dal modello di indicizzazione a partire dal testo della issue.