healthiness & fertility.
I did some research, and it's actually said that he specifically did a survey on the ages of residents in Charlottesville. He found that Charlottesville residents lived to a great age, pointing to Charlottesville being an area of "healthiness and fertility." I find this interesting, because it seems to me that Jefferson was really passionate about the location of UVA being in Charlottesville (which makes sense, considering Monticello was already here).