Novembre et. al. have recently demonstrated that if large number of genes are considered, the genetic map can be accurate enough to pin point out an individual’s origins within 500 kilometers. Using 500K SNP (Single Nucleotide Polymorphisms) in 3000 Europeans they were able to construct gene map of Europe that looked extremely similar to geographical map. Some of the landmarks of Europe are quite distinct in the genetic map.
However, one caveat is that this is probably only true for Europeans but with some amendments this may be applied to peoples from other continents as well. I am not sure. Second caveat: the sample size must be at least 6. One cannot still send one’s DNA to find out where his grandparents came from in Europe. However, with a little patience one may be able to witness a day when one can find out which village one’s grandparents came from. What a moment it would be to embrace the long lost cousins.