Graduated symbols are the best way to visualize absolute numbers like population size. Usually the area of the symbols is made proportional with the number to be displayed. This is especially important if the values are far apart.
QGIS 1.8 offers four methods to display graduated symbols. All can be found in the dialogue ‘Layer properties’, on various tabs. The next table summarizes advantages and disadvantages of these four methods. ‘Old symbology’ is not discussed here. Read More