There are two main Extension modules that support mapping in MediaWiki: Kartographer by the Wikimedia Foundation , which is used on Wikipedia, etc., and the third-party "Maps" extension .
Kartographer has much more advanced functionality but it is coded to work with the Wikimedia Foundation tile server, which has recently been closed to third-party access due to unsustainable usage . There is an open ticket for developers to make this configurable using OpenStreetMap tile server syntax . For the time being I have activated the Maps extension on this wiki, however it would be appropriate to anticipate implementing Kartographer once it is supported.
While there is visual editing support with Kartographer, advanced mapping syntax is a bit more technically involved. I don't see support for heat maps, arrow overlays, and the like but these could potentially be added somehow by the intern to be recruited by Rodolphe.
Other people have built heat maps using GeoJson data (e.g., ), which is the default format for GIS data on Wikimedia Commons as supported by Kartographer, so technically this type of data visualization should be feasible.
