The authors took SNP data from 3,000 Europeans and overlay a PCA plot of it on a map of Europe. The result is that clusters in the PCA plot roughly align with national boundaries. They are also demonstrate that:
> an individual’s DNA can be used to infer their geographic origin with surprising accuracy—often to within a few hundred kilometres.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2735096/?_escape...
The authors took SNP data from 3,000 Europeans and overlay a PCA plot of it on a map of Europe. The result is that clusters in the PCA plot roughly align with national boundaries. They are also demonstrate that:
> an individual’s DNA can be used to infer their geographic origin with surprising accuracy—often to within a few hundred kilometres.