I wanted a proportional symbols map of a quantitative variable. Following this question Proportional Symbol Formatting I tried with centroid fill and changing the size of the marker. Nevertheless this what I get using the 10m_admin_0_map_units layer from natural earth data:
As I understand each polygon should have just one marker, nevertheless they have more than one marker. I wonder if I am doing something wrong. I tried this solution since you can only work with color for the symbology method. There is no size option for polygons. I am working with Qgis 2.14.