Pete Warden, a Brit living in Boulder, CO, has put together a visualisation of relationships between US residents on Facebook. He uses only public Facebook profiles.
Facebook allows users to choose whether to make their profiles public or private. A private - or 'locked' - profile is visible in its complete form only to Facebook friends. Therefore, private profiles cannot yield this kind of information to someone who is not a friend. Obviously, Pete is not friends with everyone in the US.
Pete has also analysed the analysis on his blog, PeteSearch.
The blog analysis includes a color-coded 'relationship map' that segments the US mainland into areas of relevance, based on the Facebook profile links. It's actually a lot of fun to read what Pete thinks about the way people living in the US link to one another.
But it's the Facebook profile link map that yields most pleasure. It has clickable nodes, for each major conurbation, that yield a lot of interesting data about friends, likes and names.
For example, by clicking on the Houston, TX, conurbation link, you can see which cities are most likely to contain friends of Houstinians. Your click also shows what Houstonians most commonly are Facebook fans of, and what first names are most popular in the city.
Looking at the entire continent, the links between east and west coast are striking, along with those between people living in the major urban areas of Chicago and Atlanta.
A similar, data-rich map of Australia would be wonderful to see.
Pete has also done an international map, but this does not take into account the precise location of the Faceoook profile, just the country. The resulting visualisation, therefore, is not very accurate in terms of locality. For countries such as Australia, where most of the population lives in the south-east corner of the continent, the result is relatively data-poor.
I urge you to go and have a look at Pete's work. You'll likely spend a good 15 minutes just mooching around the graphic. Pete's blog post is not too long and is also worth visiting and reading.