Hi Fisseha Berhane ,
Try calculating it in tableau only ,you can do so .Please do not use external calculation unless you cant do it in tableau because it will reduce your performance .
It will give you almost same result and better performance i.e. NewYork is having max population and this calculation will give NewYork 100 percentile .
or better use the step wise color using advanced option and select the center accordingly or you can create square root function .
Please mark it right and helpful if this serves your purpose so that others can also get benefited & also to close the thread.
Please use square root function on population and then step wise color coding using advanced options and set center accordingly .It's working perfectly fine for me .
I was not familar with RANK_PERCENTILE . Can you share the workbook? Regarding your second comment, since my data is dynamic and the range varies significantly based on my parameter selection, I cannot use hardcoded center.