[Errigal]

I found an interesting website which displays on a map births registered by family name in France over a one hundred year period. The site itself is very useful, and what struck me was the increase in migration within France over that time. Almost every family name I chose showed a pattern of dispersal over the hundred years. Take for example the name "Castres":










This relatively rapid mixing of people from different parts of France must make racial classification more difficult each year. I would guess that this pattern of internal migration is repeated in other European countries.

http://www.genealogie.com/nom-de-famille-1/