If we're doing suggestions to improve the map, why not include a time-function?
Now the map just shows all aggregated currencies for certain areas. What about a function to select a certain year (1850) or period (1801-1900 or 3rd century BC) to see from what countries/territories/issuers you have coins. Especially nice for collectors who collect from certain periods, as to avoid issuers that did not exist at that specific time. It could also for example avoid the map-hierarchy problem mentioned by JustForFun and the Greenland-Denmark issue, as in 1990 Danish coins are indeed used in Greenland, but when you look at 1930 (or somewhere thereabout) it indeed had it's own currency (I think).
It's an idea connected to this post about creating currency-timelines: https://en.numista.com/forum/topic62879.html. So it would need extending the map with periods in which the coins were in use in certain areas. There would also be some overlap of course during certain periods/areas, but the map would at least give a more correct overview of you collection for a certain era.
And of course, you could still have an overview for all periods, like the map is today.