Here's a figure from a brand new paper on the genetics of metabolic traits in a large Finnish cohort (which I'll be posting about in more detail shortly):
On the left is a map of the counties the samples were collected from, colour-coded by geographical/linguistic group; on the right is the genetic clustering of the samples using the same colour scheme. For anyone who's been reading Razib's posts on genetic maps of Europe and East Asia, the clear message here won't come as a surprise: once you have a sufficiently large sample of markers, genes correlate with geographic ancestry with satisfying precision even within countries. And of course this precision will continue to improve with analyses that involve markers with lower frequencies (using large-scale sequencing data), which are likely to be much more informative about fine-scale geographic ancestry.
The Finns are an interesting group, being clear genetic outliers relative to most of the rest of Europe. No doubt Razib will have more to say about this map given his notorious attitudes towards the Finnish people.
Added in edit: It's worth emphasising that the individuals plotted here were only those who had both parents from the same region; see my follow-up post.
Chiara Sabatti, Susan K Service, Anna-Liisa Hartikainen, Anneli Pouta, Samuli Ripatti, Jae Brodsky, Chris G Jones, Noah A Zaitlen, Teppo Varilo, Marika Kaakinen, Ulla Sovio, Aimo Ruokonen, Jaana Laitinen, Eveliina Jakkula, Lachlan Coin, Clive Hoggart, Andrew Collins, Hannu Turunen, Stacey Gabriel, Paul Elliot, Mark I McCarthy, Mark J Daly, Marjo-Riitta JÃ¤rvelin, Nelson B Freimer, Leena Peltonen (2008). Genome-wide association analysis of metabolic traits in a birth cohort from a founder population Nature Genetics DOI: 10.1038/ng.271
In case anyone is unsure about what they mean by "linguistic group", those are traditional Finnish dialect subdivisions (the Saami were not included in this study)