Formulas for proportion charts on map I try to show pie charts on a map. Each pie chart is a marker for a settlement so the chart size depends on the population. The pie chart sectors contain information about people's nationality. I tried to figure out a right formula to show proportional charts, but I am not satisfied with the results.
Some charts are too big, others are way too small. Sometimes it's even impossible to see the chart or it's information.
Can you tell me formulas which makes good proportions between charts?
I attached a picture to make it easier to understand my problem.

Thanks for your help!
UPDATE: I forgot to mention before, the picture is the result of using logarithm on local population size.

I would suggest you to use pie charts proportional to the logarithm of local population size, rather than to the population size. This should 'improve" the proportions between charts. 
Alternatively, if the logarithmic compression is not sufficient, you could consider stronger transformations, such as double logarithm or super-logarithm.
