However, labelling such circles is problematic, specially in the case of Europe where many countries are small and close enough each other.

Is there a way to set up the label size?

This is what I am doing:

    self filteredTerritories: (self itemsByFeature: 'country') asBag sortedElements.
    gbViewBuilder := RTCountryMapBuilder newWithCentroids: self filteredTerritories.
    gbViewBuilder countries: RTMapBuilder countries.
    gbViewBuilder centroids: self filteredTerritories  named: [ : assoc | assoc key  ].
    gbViewBuilder centroids shape
        size: [ : countryAssoc | countryAssoc value  ];
        if: [ :c | c value < 10 ] fillColor: (Color green alpha: 0.5);
        if: [ :c | c value >= 10 and: c value < 50 ] fillColor: (Color yellow alpha: 0.5);
        if: [ :c | c value >= 50 ] fillColor: (Color red alpha: 0.5);       
        labelledAs: [ : c | self centroidLabel: c  ].

    gbViewBuilder color: Color veryVeryLightGray.
    gbViewBuilder scale: 1.5.
    gbViewBuilder withPopup.
    gbViewBuilder build.
    gbViewBuilder view.

Cheers,

Hernán