Bitcoin Usage Europe Map
This map, provided by http://www.Coinmap.org presents how often is bitcoin used at venues in european cities.
For the live view go to: https://coinmap.org/#/world/46.89023157/15.64453125/5
What is interesting, the bitcoin is most used in areas defined by "Blue banana" - area with the highest urbanization rates in Europe.
And here is the population density: