IMO you should put this KPI on color card, instead, and let the depth of color define the highs and lows.
You can't do that with baseline maps, but there are probably a couple of options available. For one, you could just use map shapes like this. The problem is that they won't be arranged geographically. The key is setting the mark type to map.
A second option would be using a bubble map like this. Still arranged geographically, but you're using the bubble size to indicate the measure.
A final option would require some manual work, but you could create a cartogram. That would probably require some GIS tools outside of Tableau though.