Estonia is a small country with no geographic barriers and its Estonian population is merely one million. In order to study the genetic structure of Estonia in more detail, all Estonian individuals were grouped here by their county of birth. Then, PCA was performed and the mean values of the two first PC of the counties were plotted onto the Estonian regional map (Figure 2). Surprisingly, the resulting genetic map correlates almost perfectly with the geographic map, although Estonia is only 43,400 km2 in size, and the mean area of a county only 2,900 km2. Thus, fine-scale genetic difference can be revealed by PC analysis, and the results can be useful for identification of the distant relatives.
