Meh, I guess if you know the area you can see some trends. Like in Oklahoma, Oklahoma county has about 15% for people than Tulsa county, but Tulsa is a darker red. Probably because of Union and Jenks dominating the state for so long. Tulsa County seems to be a darker red than a lot of larger counties in the region, with the exception of Texas. Union and Jenks also are two of the richest school districts in the state too, so that's probably a bigger factor than per capita.
Edit: If you go to the link and click on per capita instead of count, then you can see the true hot spots.